Document:

<PAGE>   1

                                                                   EXHIBIT 10.5

                             STOCK PLEDGE AGREEMENT

        STOCK PLEDGE AGREEMENT, dated as of December 5, 2000, between CLAYTON A.
THOMAS, JR. ("Pledgor") and NET2000 COMMUNICATIONS GROUP, INC. ("Pledgee").

                              W I T N E S S E T H:

                WHEREAS, Pledgor has delivered a Note dated December 5, 2000
(the "Note") to Pledgee, evidencing a loan in the aggregate principal amount of
up to $1,500,000 made or to be made by Pledgee to Pledgor; and

                WHEREAS, the Loan is being made pursuant to a letter agreement,
dated the date hereof, between Pledgor and Pledgee (as amended, modified or
otherwise supplemented from time to time, the "Letter Agreement"); and

                WHEREAS, as an inducement to Pledgee to make the Loan, Pledgor
has agreed to provide security for the payment of the Loan and the payment and
performance of the other obligations and indebtedness evidenced thereby and in
connection therewith;

                NOW, THEREFORE, in consideration of the premises and the
covenants set forth herein and in the Note, the parties hereto agree as follows.

                1.      Definitions. Capitalized terms used but not defined
herein and defined in the Note or the Letter Agreement are used herein as
therein defined. References to this "Agreement" shall mean this Stock Pledge
Agreement as the same may be in effect at the time such reference becomes
operative, including all amendments, modifications and supplements hereto and
any exhibits or schedules to any of the foregoing.

                2.      Pledge. In order to secure the payment and performance
in full of the Loan, all interest payable in respect thereof, and all other
amounts payable by Pledgor to Pledgee under the Note, the Letter Agreement and
under this Agreement (collectively, the "Obligations"), Pledgor hereby pledges,
assigns, grants a security interest in, transfers and delivers unto Pledgee each
of the following (the "Collateral"):

                (a)     all of Pledgor's right, title and interest in and to all
        shares (the "Pledged Shares") of capital stock described in Schedule I
        hereto and the certificates, if any, representing the Pledged Shares,
        and all dividends, cash, instruments and other property from time to
        time received, receivable or otherwise distributed in respect of or in
        exchange for any or all of the Pledged Shares;

                (b)     all other rights appurtenant to the property described
        in clause (a) above (including, without limitation, voting rights); and

<PAGE>   2

                (c)     all cash and noncash proceeds of any and all of the
        foregoing.

        Certificates representing the Pledged Shares set forth on Schedule I
hereto, accompanied by proper instruments of assignment duly executed in blank
by Pledgor, are herewith delivered to Pledgee.

                3.      Representations and Warranties. Pledgor hereby
        represents and warrants to Pledgee that as of the date hereof:

                (a)     Pledgor is the sole holder of record and beneficial
        owner of the Pledged Shares set forth on Schedule I hereto, free and
        clear of any pledge, hypothecation, assignment, lien, charge, claim,
        security interest, option, preference, priority or other preferential
        arrangement of any kind or nature whatsoever ("Lien") thereon or
        affecting the title thereto.

                (b)     Pledgor has the legal right to pledge, assign, grant a
        security interest in, transfer and deliver the Collateral to Pledgee as
        provided herein.

                (c)     This Agreement has been duly executed and delivered by
        Pledgor and constitutes the legal, valid and binding obligation of
        Pledgor, enforceable in accordance with its terms, subject to applicable
        bankruptcy, insolvency and similar laws affecting creditors' rights
        generally and subject, as to enforceability, to general principles of
        equity.

                (d)     No consent, approval, authorization or other order of
        any person, corporation, business trust, joint venture, association,
        company, partnership or government or any agency or political
        subdivision thereof (each, a "Person") (including, without limitation,
        any creditor of Pledgor) is required for (i) the execution and delivery
        of this Agreement by Pledgor or the delivery by Pledgor of the
        Collateral to Pledgee as provided herein, or (ii) the exercise by
        Pledgee of the voting or other rights provided for in this Agreement or
        the remedies in respect of the Collateral pursuant to this Agreement,
        except as may be required in connection with the disposition of the
        Collateral by laws affecting the offering and sale of securities
        generally.

                (e)     Upon the delivery to Pledgee of the certificates
        representing the Pledges Shares, Pledgee will have a valid and perfected
        security interest therein subject to no prior Lien.

                The representations and warranties set forth in this Section 3
shall survive the execution and delivery of this Agreement.

                4.      Rights of Pledgor and Pledgee.

                                     - 2 -

<PAGE>   3

                (a)     So long as the Note and any of the other Obligations are
        outstanding, Pledgee shall be entitled to exercise any and all voting
        and other consensual rights pertaining to the Pledged Shares or any part
        thereof for any purpose and Pledgor agrees that it will not exercise any
        voting and other consensual rights pertaining to the Pledged Shares
        during such time.

                (b)     Unless an Event of Default shall have occurred and be
continuing, Pledgor shall be entitled, from time to time, to collect and receive
for its own use all cash dividends (except cash dividends paid or payable in
respect of the total or partial liquidation of an issuer) paid on the Pledged
Shares; provided, however, that until actually paid, all rights to such
dividends shall remain subject to the Lien of this Agreement. All dividends
(other than cash dividends governed by the immediately preceding sentence) and
all other distributions in respect of any of the Collateral, whenever paid or
made, shall be delivered to Pledgee and held by it subject to the Lien created
by this Agreement.

                (c)     For the purposes of enabling Pledgee to exercise its
rights under this Section 3 or otherwise in connection with this Agreement,
Pledgor hereby (i) constitutes and appoints Pledgee (and any of Pledgee's
officers, employees or agents designated by Pledgee) its true and lawful
attorney-in-fact, with full power and authority to execute any notice,
assignment, endorsement or other instrument or document, and to do any and all
acts and things for and on behalf of Pledgor, which Pledgee may deem necessary
or desirable to protect, collect, realize upon and preserve the Pledged
Collateral, to enforce Pledgee's rights with respect to the Pledged Collateral
and to accomplish the purposes hereof, and (ii) revokes all previous proxies
with regard to the Pledged Collateral and appoints Pledgee as its proxyholder
with respect to the Pledged Collateral to attend and vote at any and all
meetings of the shareholders of the Companies held on or after the date of this
proxy and prior to the termination hereof, with full power of substitution to do
so and agrees, if so requested, to execute or cause to be executed appropriate
proxies therefor. Each such appointment is coupled with an interest and
irrevocable so long as the Obligations have not been paid and performed in full.
Pledgor hereby ratifies, to the extent permitted by law, all that Pledgee shall
lawfully and in good faith do or cause to be done by virtue of and in compliance
with this Section.

                (d)     Notwithstanding any provision contained in this
Agreement, Pledgee shall have no duty to exercise any of the rights, privileges
or powers afforded to it and shall not be responsible to Pledgor or any other
Person for any failure to do so or delay in doing so.

                5.      Covenants. Pledgor covenants and agrees that until the
        termination of this Agreement:

                (a)     Pledgor will not, without the prior written consent of
        Pledgee, assign this Agreement to any third party.

                (b)     Pledgor will not, without the prior written consent of
        Pledgee, sell, assign, transfer, mortgage, pledge or otherwise encumber
        any of its rights in or to the Collateral

                                     - 3 -

<PAGE>   4

        or any dividends or other distributions or payments with respect thereto
        or grant a Lien on any thereof.

                (c)     Pledgor will, at its own expense, execute, acknowledge
        and deliver all such instruments and take all such action as Pledgee
        from time to time may reasonably request in order to ensure to Pledgee
        the benefits of the first priority Lien on and to the Collateral
        intended to be created by this Agreement.

                (d)     Pledgor will defend the title to the Collateral and the
        Lien of Pledgee thereon against the claim of any Person claiming against
        or through Pledgor and will maintain and preserve such Lien so long as
        this Agreement shall remain in effect.

                6.      Additional Stock, Stock Dividends, Distributions, etc.

        If, while this Agreement is in effect, the Pledgor shall become
entitled to receive or shall receive any stock certificate (including, without
limitation, any certificate representing a stock dividend or a distribution in
connection with any reclassification, increase or reduction of capital, or
issued in connection with any reorganization), option or rights, whether as an
addition to, in substitution of, or in exchange for any shares of any Pledged
Shares, or otherwise, the Pledgor agrees to accept the same as the Pledgee's
agent and to hold the same in trust on behalf of and for the benefit of the
Pledgee and to deliver the same forthwith to the Pledgee in the exact form
received, with the endorsement of the Pledgor when necessary or appropriate,
together with undated stock powers duly executed in blank, to be held by Pledgee
as additional security for the Obligations. Any sums paid upon or in respect of
the Pledged Shares upon the liquidation or dissolution of the issuer thereof
shall be paid over to the Pledgee to be held by it in trust as additional
security for the Obligations. In case any distribution of capital shall be made
on or in respect of the Pledged Shares or any property shall be distributed upon
or with respect to the Pledged Shares pursuant to the recapitalization or
reclassification of the capital of the issuer thereof pursuant to the
reorganization of such issuer, the property so distributed shall be delivered to
the Pledgee to be held by it as additional security for the Obligations. All
sums of money and property so paid or distributed in respect of the Pledged
Shares which are received by the Pledgor shall, until paid or delivered to the
Pledgee, be held by the Pledgor in trust as additional security for the
Obligations.

                7.      Remedies.

                (a)     Upon the occurrence of an Event of Default, then or at
        any time during the continuance of such occurrence, Pledgee is hereby
        authorized and empowered, at its election, (i) to transfer and register
        in its or its nominee's name the whole or any part of the Collateral,
        (ii) to demand, sue for, collect, receive and give acquittance for any
        and all cash dividends or other distributions or monies due or to become
        due upon or by virtue thereof, and to settle, prosecute or defend any
        action or proceeding with respect thereto, (iii) to sell in one or more
        sales the whole or any part of the Collateral or otherwise to transfer
        or assign the same, applying the proceeds therefrom to the payment of
        the Obligations in such order as Pledgee shall determine, and (iv)
        otherwise to act with

                                     - 4 -
<PAGE>   5

        respect to the Collateral or the proceeds thereof as though Pledgee were
        the outright owner thereof, Pledgor hereby irrevocably constituting
        Pledgee as its proxy and attorney-in-fact, with full power of
        substitution to do so.

                (b)     Pledgee shall give Pledgor not less than ten days' prior
        written notice of the time and place of any sale or other intended
        disposition of any of the Collateral except any Collateral that
        threatens to decline speedily in value or is of a type customarily sold
        on a recognized market. Pledgor agrees that such notice constitutes
        "reasonable notification" within the meaning of Section 9-504(3) of the
        Uniform Commercial Code. Any sale shall be made at a public or private
        sale at Pledgee's place of business, or at any public building in the
        City of New York to be named in the notice of sale, either for cash or
        upon credit or for future delivery at such price as Pledgee may deem
        fair, and, to the extent permitted by applicable law, Pledgee may be the
        purchaser of the whole or any part of the Collateral so sold and hold
        the same thereafter in its own right free from any claim of Pledgor or
        any right or equity of redemption, which right or equity is hereby
        waived and released. Each sale shall be made to the highest bidder, but
        Pledgee reserves the right to reject any and all bids at such sale
        which, in its sole discretion, it shall deem inadequate. Except as
        otherwise herein specifically provided for, demands of performance,
        notices of sale, advertisements and the presence of property at sale are
        hereby waived and any sale hereunder may be conducted by an auctioneer
        or any officer of agent of Pledgee.

                (c)     If, at the original time or times appointed for the sale
        of the whole or any part of the Collateral, either (i) the highest bid,
        if there be but one sale, shall be inadequate to discharge in full all
        the Obligations, or (ii) if the Collateral be offered for sale in lots,
        if at any of such sales the highest bid for the lot offered for sale
        would indicate to Pledgee in its sole discretion the unlikelihood of the
        proceeds of the sales of the whole of the Collateral being sufficient to
        discharge all the obligations, then in either such event Pledgee may, on
        one or more occasions, postpone any of said sales by public announcement
        at the time of sale. In the event of any such postponement, Pledgee
        shall give Pledgor notice of such postponement.

                (d)     If, at any time when Pledgee shall determine to exercise
        its right to sell the whole or any part of the Collateral hereunder,
        such Collateral or the part thereof to be sold shall not, for any reason
        whatsoever, be effectively registered under the Security Act of 1933, as
        amended (the "Act"), Pledgee may, in its sole and absolute discretion
        (subject only to applicable requirements of law), sell such Collateral
        or part thereof by private sale in such manner and under such
        circumstances as Pledgee may deem necessary or advisable, but subject to
        the other requirements of this Section 7, and shall not be required to
        effect such registration or to cause the same to be effected. Without
        limiting the generality of the foregoing, in any such event Pledgee in
        its sole and absolute discretion may (a) proceed to make such private
        sale notwithstanding that a registration statement for the purpose of
        registering such Collateral or part thereof could be or shall have been
        filed under the Act (or similar statute), (b) approach and negotiate
        with a single possible purchaser to effect such sale, (c) restrict such
        sale to a purchaser who will represent and agree that such purchaser is
        purchasing for its own account, for investment and not with a

                                     - 5 -
<PAGE>   6

        view to the distribution or sale of such Collateral or part thereof, and
        (d) require that any sale hereunder (including a sale at auction) be
        conducted subject to restrictions (i) as to the financial sophistication
        and ability of any Person permitted to bid or purchase at sale, (ii) as
        to the content of legends to be placed upon any certificates
        representing the Collateral sold in such sale, including restrictions on
        future transfer thereof, (iii) as to the representations required to be
        made by each Person bidding or purchasing at such sale relating to that
        Person's access to financial information about Pledgor, the issuer of
        the Pledged Shares or Pledgee, such Person's intentions as to the
        holding of the Collateral so sold for investment, for its own account,
        and not with a view to the distribution thereof, and (iv) as to such
        other matters as Pledgee may, in its sole discretion, deem necessary or
        appropriate in order that such sale (notwithstanding any failure so to
        register) may be effected in compliance with the Uniform Commercial Code
        and other laws affecting the enforcement of creditors' rights and the
        Act (or similar statute) and all applicable state securities laws.
        Pledgor will execute and deliver such documents and take such other
        action as Pledgee deems necessary or advisable in order that any such
        sale may be made in compliance with law.

                (e)     In the event of any such sale under the circumstances
        described in this Section 7, Pledgee shall incur no responsibility or
        liability for selling the whole or any part of the Collateral at a price
        which Pledgee may deem reasonable under the circumstances,
        notwithstanding the possibility that a substantially higher price might
        be realized if the sales were deferred until after registration as
        aforesaid. Pledgor hereby acknowledges that any sale of any of the
        Collateral which has not been registered under the Act may be for a
        price less that which might have been obtained had the Collateral been
        registered under the Act;

                (f)     Pledgor agrees that it will not at any time plead, claim
        or take the benefit of any appraisal, valuation, stay, extension,
        moratorium or redemption law now or hereafter in force in order to
        prevent or delay the enforcement of this Agreement, or the absolute sale
        of the whole or any part of the Collateral or the possession thereof by
        any purchaser at any sale hereunder, and Pledgor waives the benefit of
        all such laws to the extent it lawfully may do so. Pledgor agrees that
        it will not interfere with any right, power and remedy of Pledgee
        provided for in this Agreement or now or hereafter existing at law or in
        equity or by statute or otherwise, or the exercise or beginning of the
        exercise by Pledgee of any one or more such rights, powers or remedies.
        No failure or delay on the part of Pledgee to exercise any such right,
        power or remedy, and no notice or demand which may be given to or made
        upon Pledgor by Pledgee with respect to any such remedies, shall operate
        as a waiver thereof, or limit or impair Pledgee's right to take any
        action or to exercise any power or remedy hereunder without notice or
        demand, or prejudice its rights as against Pledgor in any respect.

        8.      Application of Proceeds. The proceeds of any sale of, or other
realization upon, all or any part of the Collateral and any cash held shall be
applied by the Pledgee in the following order of priorities:

                                     - 6 -
<PAGE>   7

                first, to payment of the expenses of such sale or other
        realization, including reasonable compensation to agents and counsel for
        the Pledgee, and all expenses, liabilities and advances incurred or made
        by the Pledgee in connection therewith;

                second, to the payment of the Obligations;

        third, to payment to the Pledgor or its successors or assigns, or as a
        court of competent jurisdiction may direct, of any surplus then
        remaining from such proceeds.

        9.      Exoneration of Pledgee. Other than the exercise of reasonable
care in the custody and preservation of the Collateral, Pledgee shall have no
duty with respect thereto. Pledgee shall be deemed to have exercised reasonable
care in the custody and preservation of the Collateral in its possession if the
Collateral is accorded treatment substantially equal to that which it accords
its own property, and shall not be liable or responsible for any loss or damage
to any of the Collateral, or for any diminution in the value thereof, by reason
of the act or omission of any agent or bailee selected by Pledgee in good faith.

        10.     Waiver. No delay on Pledgee's part in exercising any power of
sale or other right hereunder, and no notice or demand which may be given to or
made upon Pledgor by Pledgee with respect to any power of sale or other right
hereunder, shall constitute a waiver thereof, or limit or impair Pledgee's right
to take any action or to exercise any power of sale or any other right
hereunder, without notice or demand, or prejudice Pledgee's rights as against
Pledgor in any respect.

        11.     Termination. At such time as (a) all Obligations have been fully
satisfied and (b) the Note shall have been terminated, Pledgee shall deliver to
Pledgor the Collateral remaining after giving effect to the exercise of
Pledgee's rights and remedies hereunder at the time subject to this Agreement
and all instruments of assignment executed in connection therewith, free and
clear of the Lien hereof and all of Pledgor's obligations hereunder shall
thereupon terminate. When so released, such Collateral shall be free and clear
of any lien or encumbrance hereunder.

        12.     Release. Pledgor consents and agrees that Pledgee may at any
time, or from time to time, in Pledgee's sole discretion, exchange, release
and/or surrender all or any of the Collateral, or any part(s) thereof, by
whomever deposited, which is now or may hereafter be held by Pledgee in
connection with all or any of the Obligations, all in such manner and upon such
terms as Pledgee may deem proper, and without notice to or further assent from
Pledgor, it being hereby agreed that Pledgor shall be and remain bound by this
Agreement, irrespective of the existence, value or condition of any collateral
and notwithstanding (i) any such exchange, release and/or surrender and/or (ii)
any settlement, compromise, surrender, release, renewal or extension of any or
all of the Obligations, and/or (iii) that the Obligations may at any time or
from time to time exceed the aggregate principal amount outstanding pursuant to
the Note.

        13.     Expenses. Pledgor will reimburse Pledgee for all expenses
(including reasonable expenses for legal services of every kind) of, or
incidental to the preparation or

                                     - 7 -

<PAGE>   8

enforcement of any of the provisions of, this Agreement or any actual or
attempted sale, or any exchange, enforcement, collection, compromise or
settlement of any of the Collateral and for the care of the Collateral and
defending or asserting the rights and claims of Pledgee in respect of the
Collateral, by litigation or otherwise, including but not limited to expenses of
insurance and the fees and expenses of counsel for Pledgee. All such expenses
shall be deemed additional Obligations.

        14.     Miscellaneous.

                (a)     Pledgee may execute any of its duties hereunder by or
        through agents or employees. Pledgee may consult with legal counsel and
        any action taken or suffered in good faith in accordance with the advice
        of such counsel shall be full justification and protection to it.

                (b)     Neither Pledgee nor any of its officers, directors,
        employees, agents or counsel shall be liable for any action lawfully
        taken or omitted to be taken by it or them hereunder or in connection
        herewith, except for their own gross negligence or willful misconduct
        and Pledgee shall not be liable for any error of judgment made by it in
        good faith.

                (c)     This Agreement shall be binding upon Pledgor and its
        successors and assigns, and shall inure to the benefit of, and be
        enforceable by, Pledgee and its successors, transferees and assigns,
        except that the Pledgor shall not have the right to assign its rights
        hereunder or any interest herein (and any such attempted assignment
        shall be void). None of the terms or provisions of this Agreement may be
        waived, altered, modified or amended except in writing duly signed for
        and on behalf of Pledgee and Pledgor.

                (d)     THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED AND
        ENFORCED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK
        APPLICABLE TO CONTRACTS MADE AND PERFORMED IN SUCH STATE.

                (e)     Pledgor hereby waives personal service or any and all
        process upon Pledgor, and consents that all such service of process be
        made by registered mail directed to Pledgor at the address stated in
        Section 16 hereof and service so made shall be deemed to be completed
        five (5) Business Days after the same shall have been deposited in the
        United States mails, postage prepaid. To the extent permitted by law,
        Pledgor waives trial by jury and waives any objection to venue of any
        action instituted hereunder.

                15.     Further Assurances; Pledgee May Perform.

                (a)     At Pledgor's expense, Pledgor will do all such acts, and
        will furnish to Pledgee all such financing statements, certificates,
        legal opinions and other documents and will do or cause to be done all
        such other things as Pledgee may reasonably request

                                     - 8 -
<PAGE>   9

        from time to time in order to give full effect to this Agreement and to
        secure the rights intended to be granted to Pledgee hereunder. To the
        extent permitted by applicable law, Pledgor hereby authorizes Pledgee to
        execute and file, in the name of Pledgor or otherwise, Uniform
        Commercial Code financing statements (which may be photocopies of this
        Agreement) which Pledgee in its sole discretion may deem necessary or
        appropriate.

                (b)     If Pledgor fails to perform any act required by this
        Agreement, Pledgee may perform, or cause performance of, such act, and
        the expenses of Pledgee incurred in connection therewith shall be
        governed by Section 13 hereof.

        16.     Notices. All notices, requests and demands to or upon the
respective parties hereto to be effective shall be in writing (including by
telecopy) and, unless otherwise expressly provided herein, shall be deemed to
have been duly given or made when delivered by hand, or, in the case of telecopy
notices, when sent (with confirmation received), addressed as follows or to such
other address as may be hereafter notified by the respective parties hereto:

                (a)     If to Pledgee, at

                        Net2000 Communications Group, Inc.
                        2180 Fox Mill Road
                        Herndon, VA  20170
                        Attention: Donald Clarke
                        Telecopier: (703) 654-2025

                (b)     If to Pledgor, at

                        Mr. Clayton A. Thomas, Jr.
                        811 Water Place
                        Alexandria, Virginia  22314
                        Telecopier No.:

               Failure to comply with the provisions set forth above with
respect to the delivery of copies shall not impair the validity of any notice
otherwise complying with the terms hereof.

                17.     Severability. Any provision of this Agreement which is
prohibited or unenforceable in any jurisdiction shall not invalidate the
remaining provisions hereof, and any such prohibition or unenforceability in any
jurisdiction shall not invalidate or render unenforceable such provision in any
other jurisdiction.

                18.     Counterparts. This Agreement may be executed in any
number of counterparts and by the different parties hereto on separate
counterparts, each of which when so

                                     - 9 -

<PAGE>   10

executed and delivered shall be an original, but all of which together shall
constitute one and the same instrument.

                19.     Section Headings. The section headings used in this
Agreement are for convenience of reference only and are not to effect the
construction hereof or be taken into consideration in the interpretation hereof.

                                     - 10 -
<PAGE>   11

               IN WITNESS WHEREOF, the parties hereto have caused this Stock
Pledge Agreement to be duly executed as of the date first above written.

                                    /s/Clayton A. Thomas, Jr.
                             -------------------------------------------
                             Clayton A. Thomas, Jr., as Pledgor

                             Net2000 Communications Groups, Inc., as Pledgee

                             By:    /s/Donald Clarke
                                ----------------------------------------
                                    Donald Clarke
                                    Chief Financial Officer

                                     - 11 -

<PAGE>   12

COMMONWEALTH OF VIRGINIA)
                        )       ss:
COUNTY OF FAIRFAX       )

        On this 8th day of December, 2000, before me personally appeared CLAYTON
A. THOMAS, JR., to me known to be the person who executed the foregoing
instrument and who being by me duly sworn, did depose and say that he resides at
811 Water Place, Alexandria, Virginia and that he signed his name to the
foregoing instrument.

               SEAL
                                     /s/Jennifer S. Fabris
                                     -------------------------------------------
                                     NOTARY PUBLIC

My commission expires on:  5/31/2004

                                     - 12 -
<PAGE>   13

                                                                      Schedule I
                                                                        to Stock
                                                                Pledge Agreement

                                      Stock
<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------
Issuer                            Number and Class of Shares      Certificate(s) No.
-----------------------------------------------------------------------------------------------
<S>                               <C>                             <C>
-----------------------------------------------------------------------------------------------
Net2000 Communications, Inc.      2,466,875 shares of common      074
                                  stock                           137
-----------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------
</TABLE>

                                     - 13 -<PAGE>   1
                                                                 EXHIBIT 10.5.1

                    First Amendment to Stock Pledge Agreement

        This First Amendment to the Stock Pledge Agreement is dated January 26,
2001 and entered into by and between Clayton A. Thomas, Jr. ("Pledgor") and
Net2000 Communications Group, Inc. ("Pledgee").

        WHEREAS, Pledgor has delivered a Note dated December 5, 2000 to Pledgee,
evidencing a loan in the aggregate principal amount of up to $1,500,000 made or
to be made to Pledgee by Pledgor; and

        WHEREAS, as an inducement to Pledgee to make the loan, Pledgor agreed to
provide security for the payment of the loan and the payment and performance of
the other obligations and indebtedness evidenced thereby and in connection
therewith;

        WHEREAS, on December 5, 2000, the parties entered into a Stock Pledge
Agreement ("Agreement") under which Pledgor pledged, granted a security interest
in, transferred, and delivered unto Pledgee all of Pledgor's right, title, and
interest in 2,466,875 shares of Net2000 Communications, Inc. common stock
("Pledged Shares").

        WHEREAS, the parties wish to amend the Agreement and reduce to one
million (1,000,000) shares the amount of Pledged Shares.

        NOW, THEREFORE, the parties agree as follows:

1.      Schedule I to the Agreement is hereby deleted and replaced with the
revised Schedule I attached hereto.

2.      Pledgee hereby releases its security interest in the 1,446,875 shares of
Net2000 Communications, Inc. common stock which are not listed on revised
Schedule I attached hereto.

3.      All other terms, conditions, and obligations of the Agreement shall
remain in full force and effect unless amended in writing and signed by both
parties.

        IN WITNESS WHEREOF, the parties hereto have caused this First Amendment
to be effective as of January 26, 2001.

NET2000 COMMUNICATIONS GROUP, INC.          /s/Clayton A. Thomas, Jr.
  AS PLEDGEE                                ----------------------------
                                            CLAYTON A. THOMAS, JR.,
                                              AS PLEDGOR

BY: /s/Donald Clarke
    -------------------------
    Donald Clarke
    Chief Financial Officer

<PAGE>   2

                      SCHEDULE I TO STOCK PLEDGE AGREEMENT

                                      Stock

<TABLE>
<CAPTION>
-------------------------------------------------------------------------------------------
            Issuer                Number and Class of Shares        Certificate(s) No.
-------------------------------------------------------------------------------------------
<S>                               <C>                               <C>
-------------------------------------------------------------------------------------------
 Net2000 Communications, Inc.     1,000,000 shares of common             N2K 0296
                                            stock                        N2K 0297
-------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------
</TABLE>

<PAGE>   3

COMMONWEALTH OF VIRGINIA)
                        )    ss:
COUNTY OF FAIRFAX       )

        On this 11th day of March, 2001 before me personally appeared CLAYTON A.
THOMAS, JR., to me known to be the person who executed the foregoing instrument
and who being by me duly sworn, did depose and say that he signed his name to
the foregoing instrument.

        SEAL                                /s/Catherine Esser
                                            ----------------------------
                                            NOTARY PUBLIC

My commission expires on:  11/30/2004

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00024-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00024-of-00352.parquet"}]]