<PAGE>

                                                                   Exhibit 10.40

                                              Lease No. WT-3519-NP-7,8,9 (1497A)
                                              Supplement No. 1

                             SUPPLEMENTAL AGREEMENT

            THIS AGREEMENT, made as of August 15, 2000 by and between THE PORT
AUTHORITY OF NEW YORK AND NEW JERSEY (hereinafter called the "Port Authority")
and CREDIT SUISSE FIRST BOSTON CORPORATION (hereinafter called the "Lessee"),

            WITNESSETH, That:

            WHEREAS, the Port Authority and the Lessee, heretofore and as of
December 31, 1998, entered into an agreement of lease identified by the above
Port Authority Lease Number (which agreement of lease, as the same may have
heretofore been supplemented and amended, is hereinafter called the "Lease")
covering premises at the Port Authority World Trade Center, in the Borough of
Manhattan, City, County and State of New York, as more particularly described in
the Lease;

            WHEREAS, the Port Authority and the Lessee desire to add to the
premises under the Lease and to amend the Lease in certain other respects;

            NOW, THEREFORE, for and in consideration of the covenants and mutual
agreements herein contained, the Port Authority and the Lessee hereby agree as
follows:

            1. (a) In addition to the premises heretofore let to the Lessee
under the Lease, the letting of which shall continue in full force and effect,
and subject to all of the terms, provisions, covenants and conditions of the
Lease, the Port Authority hereby lets to the Lessee and the Lessee hereby hires
and takes from the Port Authority at the Port Authority World Trade Center in
the Borough of Manhattan, City, County and State of New York: (a) the space
shown in diagonal hatching on the sketch attached hereto, hereby made a part
hereof and marked "Exhibit A-5", together with the fixtures, improvements and
other property of the Port Authority located or to be located therein or
thereon, sometimes hereinafter referred to as "Area A-5"; (b) the space shown in
diagonal hatching on the sketch attached hereto, hereby made a part hereof and
marked "Exhibit A-6", together with the fixtures, improvements and other
property of the Port Authority located or to be located therein or thereon,
sometimes hereinafter referred to as "Exhibit A-6"; and (c) the space shown in
diagonal hatching on the sketch attached hereto, hereby made a part hereof and
marked "Exhibit A-7", together with the fixtures, improvements and other
property of the Port Authority located or to be located therein or thereon,
sometimes hereinafter referred to as "Area A-7". (Area A-5, Area A-6 and Area
A-7 being hereinafter collectively referred to as the "Additional Office
Premises".) Area A-5 and Area A-6 shall be and become a part of the premises
under the Lease for a term commencing at 12:01 o'clock A.M. on August 15, 2000
and Area A-7 shall be and become a part of the premises under the Lease for a
term commencing at 12:01 o'clock A.M. on October 1, 2000 (as said dates may be
postponed


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<PAGE>

from time-to-time pursuant to the provisions of subparagraph (b) of this
paragraph 1) (the said dates or postponed dates being hereinafter referred to as
the "Area 5/6 Effective Date" and the "Area A-7 Effective Date", respectively)
and each then continuing throughout the balance of the term of the letting under
the Lease. The Port Authority and the Lessee hereby acknowledge that the
Additional Office Premises constitutes non-residential real property.

                  (b) If on August 15, 2000, Area A-5 and/or Area A-6 is not
available or ready for occupancy or use by the Lessee and/or if on October 1,
2000, Area A-7 is not available or ready for occupancy or use by the Lessee, by
reason of the fact that said Areas or any one of them, or any part thereof, or
any part of the World Trade Center are in the course of construction, repair,
alteration or improvement or by reason of the fact that the occupant thereof
failed or refused to deliver possession or by reason of any causes or conditions
beyond the control of the Port Authority, the Port Authority may postpone the
letting of such Area or Areas or part thereof and the Port Authority shall not
be subject to any liability for such postponement or failure to give possession
on such date. No such postponement or failure to give possession of any Area or
part thereof on such date shall affect the validity of the Lease or this
Agreement or the obligations of the Lessee under either the Lease or this
Agreement, except that the Area A-5/6 Effective Date and/or the Area A-7
Effective Date, as the case may be, shall be deemed to be the date possession of
such area is tendered to the Lessee as set forth in the following sentence. In
the event of such postponement, possession of any Area or part thereof shall be
tendered by the Port Authority to the Lessee by notice given at least five (5)
days prior to the effective date of the tender. In the event that notice of
tender for any Area or part thereof is not given for possession thereof to
commence on or before August 15, 2001, then the letting of said Area or part
thereof under this Agreement shall be deemed canceled, and each party shall and
does release and discharge the other party from any and all claims or demands
with respect thereto based on this Agreement, or a breach or alleged breach
thereof.

            2. The Lessee shall use the Additional Office Premises solely for
the purpose set forth in Section 3 of the Lease and for no other purpose or
purposes whatsoever.

            3. In addition to the basic rental otherwise payable under the
Lease, the Lessee shall pay to the Port Authority a basic rental for the
Additional Office Premises as follows:

                  (a) With respect to Area A-5 and Area A-6:

                        (i) During the period from and after the one hundred
      twentieth (120th) day following the Area A-5/6 Effective Date (hereinafter
      referred to as the "Area A-5/6 Rent Commencement Date") through and
      including the day preceding the fifth anniversary of the Area A-5/6
      Effective Date, at the rate of One Million Two Hundred Forty-two Thousand
      Nine Hundred Sixty Dollars and No Cents ($1,242,960.00) per annum, in
      advance in monthly installments of One Hundred Three Thousand Five Hundred
      Eighty Dollars and No Cents ($103,580.00) each, on the one hundred
      twentieth (120th) day following the Area 5/6 Effective Date and on the
      first day of each calendar month thereafter


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      through and including the day preceding the fifth anniversary of the Area
      A-5/6 Effective Date.

                        (ii) During the period from and after the fifth
      anniversary of the Area A-5/6 Effective Date through and including the day
      preceding the tenth anniversary of the Area A-5/6 Effective Date, at the
      rate of One Million Three Hundred Sixty-seven Thousand Eight Hundred
      Sixty-eight Dollars and No Cents ($1,367,868.00) per annum, in advance in
      monthly installments of One Hundred Thirteen Thousand Nine Hundred
      Eighty-nine Dollars and No Cents ($113,989.00) each, on the fifth
      anniversary of the Area A-5/6 Effective Date and on the first day of each
      calendar month thereafter through and including the day preceding the
      tenth anniversary of the Area A-5/6 Effective Date.

                        (iii) During the period from and after the tenth
      anniversary of the Area A-5/6 Effective Date and through the balance of
      the term of the letting, at the rate of One Million Four Hundred
      Ninety-two Thousand Seven Hundred Eighty-eight Dollars and No Cents
      ($1,492,788.00) per annum, in advance in monthly installments of One
      Hundred Twenty-four Thousand Three Hundred Ninety-nine Dollars and No
      Cents ($124,399.00) each, on the tenth anniversary of the Area A-5/6
      Effective Date and on the first day of each calendar month thereafter
      throughout the balance of the term of the letting.

                  (b) With respect to Area A-7:

                        (i) During the period from and after the one hundred
      twentieth (120th) day following the Area A-7 Effective Date (hereinafter
      referred to as the "Area A-7 Rent Commencement Date") through and
      including the day preceding the fifth anniversary of the Area A-7
      Effective Date, at the rate of One Hundred Twenty-two Thousand Five
      Hundred Eighty Dollars and No Cents ($122,580.00) per annum, in advance in
      monthly installments of Ten Thousand Two Hundred Fifteen Dollars and No
      Cents ($10,215.00) each, on the Area A-7 Rent Commencement Date and on the
      first day of each calendar month thereafter through and including the day
      preceding the fifth anniversary of the Area A-7 Effective Date.

                        (ii) During the period from and after the fifth
      anniversary of the Area A-7 Effective Date through and including the day
      preceding the tenth anniversary of the Area A-7 Effective Date, at the
      rate of One Hundred Thirty-four Thousand Nine Hundred Four Dollars and No
      Cents ($134,904.00) per annum, in advance in monthly installments of
      Eleven Thousand Two Hundred Forty-two Dollars and No Cents ($11,242.00)
      each, on the fifth anniversary of the Area A-7 Effective Date and on the
      first day of each calendar month thereafter through and including the day
      preceding the tenth anniversary of the Area A-7 Effective Date.


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<PAGE>

                        (iii) During the period from and after the tenth
      anniversary of the Area A-7 Effective Date and through the balance of the
      term of the letting, at the rate of One Hundred Forty-seven Thousand Two
      Hundred Twenty-eight Dollars and No Cents ($147,228.00) per annum, in
      advance in monthly installments of Twelve Thousand Two Hundred Sixty-nine
      Dollars and No Cents ($12,269.00) each, on the tenth anniversary of the
      Area A-7 Effective Date and on the first day of each calendar month
      thereafter throughout the balance of the term of the letting.

                  (c) If the Area A-5/6 Rent Commencement Date or the Area A-7
Rent Commencement Date is other than the first day of a calendar month, the
installment of basic rental payable on such date shall be the amount of the
monthly installment stated in subparagraph (a)(1) or (b)(1) above, as
applicable, multiplied by a fraction the numerator of which shall be the number
of days from the Area A-5/6 Rent Commencement Date or the Area A-7 Rent
Commencement Date, as applicable, to the last day of the calendar month in which
said date shall fall (both days inclusive) and the denominator of which shall be
the number of days in that calendar month. In the event the fifth and tenth
anniversaries of the Area A-5/6 Effective Date or the Area A-7 Effective Date,
respectively, shall occur on a day other than the first day of a calendar month,
then, in lieu of the monthly installment of basic rental payable as hereinabove
provided on each such anniversary, there shall be payable in advance on the
effective date of each such anniversary an installment of rental equal to
one-twelfth of the amount by which the annual basic rental is then being
increased multiplied by a fraction the numerator of which shall be the number of
days from each such anniversary to the end of the calendar month in which such
anniversary shall fall and the denominator of which shall be the number of days
in that calendar month.

                  (d) In addition to the basic rental for the Additional Office
Premises set forth in subparagraph (a) and (b), above, and in addition to the
additional basic rental set forth for the portions of the premises shown on
Exhibits A, A-1, A-2, A-2A, A-2B and A-3, the Lessee shall pay additional basic
rental for the Additional Office Premises in accordance with the provisions of
Schedule A attached to the Lease, except that from and after the Area A-5/6
Effective Date or the Area A-7 Effective Date, as applicable, and with respect
only to Area A-5, Area A-6 or Area A-7, as applicable, subparagraph (d) of
paragraph 1 of Schedule A attached to the Lease shall be amended to provide that
"Tax Base" shall mean the annual per rentable square foot factor finally
established to be the annual per rentable square foot factor to be used in
computing payments in lieu of taxes for the tax year beginning July 1, 2000; (2)
subparagraph (g) of paragraph 1 of Schedule A shall be deemed amended to provide
that "Basic Wage Rate" shall mean the wage rate in effect in January 1, 2000 and
(3) subparagraph (h) of paragraph 1 of Schedule A shall be amended to provide
that "Rentable Square Feet in the Premises" shall be deemed to mean 245,692
square feet, consisting of 115,559 square feet as to the portion of the premises
shown on Exhibit A, 63,223 square feet as to the portion of the premises shown
on Exhibit A-1, 37,020 square feet as to the portion of the premises shown on
Exhibit A-2, 2,442 square feet as to the portion of the premises shown on
Exhibit A-3, 22,319 square feet as to the portion of the premises shown on
Exhibit A-5, 2,665 square feet as to the portion of the premises


                                       4
<PAGE>

shown on Exhibit A-6, and 2,464 square feet as to the portion of the premises
shown on Exhibit A-7.

            4. The Lessee has thoroughly examined and inspected Areas A-5, A-6
and A-7, respectively, and has found each of them to be in good order and repair
and suitable for the Lessee's operations hereunder and agrees to take the said
Areas A-5, A-6 and A-7, respectively, in the condition it is in when vacated by
the occupant or occupants thereof and turned over to the Lessee by the Port
Authority. The Lessee hereby expressly acknowledges that it has not relied upon
any representation or statement of the Port Authority or of its Commissioners,
officers, agents or employees as to the condition or as to the suitability of
said Areas A-5, A-6 and A-7 for the operations permitted thereon by this
Agreement. The Lessee hereby agrees that except in accordance with Section 12 of
the Lease, the Lessee shall not erect any structures, make any modifications,
alterations, additions, improvements, repairs or replacements or do any
construction work on or to the Additional Office Premises (other than trade
fixtures, removable without material injury to the premises and Minor Work as
defined in paragraph (k) of said Section 12) without the prior written consent
of the Port Authority. The Port Authority and the Lessee agree that all such
construction work on or to the Additional Office Premises shall be governed by
and performed subject to the terms and conditions of paragraphs (a) through (o)
inclusive of Section 12 of the Lease except that with respect to construction
work on the Additional Office Premises only, subparagraph (m) shall be deemed
amended by changing the words and numbers appearing in subparagraph (ii) thereof
from Nine Million Seven Hundred Eleven Thousand Ninety Dollars and No Cents
($9,711,090.00) to Seven Hundred Eleven Thousand Eight Hundred Forty-five
Dollars and No Cents ($711,845.00).

            5. The provision of Section 31 of this Lease titled "Additional
Provisions Relating to Taxes" shall apply with full force and effect to the
Additional Office Premises hereunder except as follows:

                  (a) Subparagraph (a)(i) of Section 31 shall be deemed amended
to read, with respect to the Additional Office Premises only, as follows:

                  "(i) The annual basic rental thereafter payable by the Lessee
            for the Additional Office Premises shall be increased by the total
            of the following amounts: (1) the annual rate of additional basic
            rental under Paragraph 2 of this Schedule A payable by the Lessee as
            of July 1 immediately preceding such transfer of title to the
            private space, and (2) an annual amount equal to the product
            obtained by multiplying the total number of rentable square feet in
            the Additional Office Premises as of the effective date of such
            transfer of title by the lesser of (x) the sum of One Dollar and
            Twenty-five Cents ($1.25) or (y) the excess of (i) the annual per
            rentable square foot amount of Taxes first payable after title to
            the private space is transferred, based upon the amount of the full
            assessment thereof and the full amount of the tax rate generally
            applicable whether or not the transferee shall be obligated to pay
            such full amount of Taxes in the first Tax Year following such
            transfer of title over (ii) the annual per rentable square foot
            factor for the Tax Year in which such transfer of title to the
            private space occurs."


                                       5
<PAGE>

                  (b) The definition of "Tax Base" appearing in Schedule A as
amended in subparagraph (ii) of paragraph (a) of Section 31 of the Lease shall
be deemed amended to read with respect to the Additional Office Premises only,
as follows:

                        "(b) `Tax Base' shall mean the greater of the following
                  amounts: (i) the amount established as the Tax Base pursuant
                  to the provisions of subparagraph (d) of paragraph 1 of
                  Schedule A prior to the transfer of title to the private space
                  plus the quotient obtained by dividing the increase in the
                  annual basic rental resulting from the application of the
                  formula in subdivision (i) of paragraph (a) of this Section 31
                  of the Lease by the number of rentable square feet in the
                  Additional Office Premises as of the July 1st immediately
                  preceding such transfer of title or (ii) the full annual
                  amount of Taxes that would first be payable after title to the
                  private space is transferred and which reflects such transfer
                  to private ownership based upon the amount of the full
                  assessment thereof (as opposed to any interim or transitional
                  assessment) and the full amount of the rate generally
                  applicable whether or not the owner shall be obligated to pay
                  such full amount of Taxes."

                  (c) Subparagraphs (i) and (ii) of paragraph (b) of Section 31
shall be deemed amended to read, with respect to the Additional Office Premises
only, as follows:

                  "(i) The annual basic rental thereafter payable by the Lessee
            for the Additional Office Premises shall be increased by the total
            of the following amounts: (1) the annual rate of additional basic
            rental under Paragraph 2 of this Schedule A payable by the Lessee as
            of July 1 immediately preceding such transfer of the Port
            Authority's interest in the Building or in the portion thereof of
            which the premises is a part, and (2) an annual amount equal to the
            product obtained by multiplying the total number of rentable square
            feet in the Additional Office Premises as of the effective date of
            such transfer of title by the lesser of (x) the sum of One Dollar
            and Twenty-five Cents ($1.25) or (y) the excess of (i) the annual
            per rentable square foot amount of payments in lieu of taxes first
            payable after such transfer, based upon the amount of the full
            assessment thereof and the full amount of the annual per rentable
            square foot factor generally applicable whether or not the
            transferee shall be obligated to pay such full amount in the first
            Tax Year following such transfer of title over (ii) the annual per
            rentable square foot factor for the Tax Year in which such transfer
            of the Port Authority's interest in the Building or in the portion
            thereof of which the premises is a part occurs."

                  "(ii) The Lessee shall continue to pay additional basic rental
            to the Port Authority in accordance with the provisions of Schedule
            A but the definition of "Tax Base" as defined in paragraph (d) of
            Schedule A shall be amended as follows: "Tax Base" shall mean the
            greater of the following amounts: (i) the amount established as the
            Tax Base pursuant to the provisions of subparagraph (d) of paragraph
            1 of Schedule A prior to the transfer of title to the private space
            plus the quotient obtained by dividing the increase in the annual


                                       6
<PAGE>

            basic rental resulting from the application of the formula in
            subdivision (i) of paragraph (a) of this Section 31 of the Lease by
            the number of rentable square feet in the Additional Office Premises
            as of the July 1st immediately preceding such transfer of title or
            (ii) the annual per rentable square foot factor finally established
            to be the annual per rentable square foot factor to be used in
            computing payments in lieu of taxes for the period immediately
            following the transfer of the Port Authority's interest in the
            building of which the premises is a part, or a portion thereof."

            6. The provisions of Paragraph C of Section 48 of the Lease shall
not apply to Area A-5 and any exercise by the Lessee of its right thereunder to
terminate the entire premises or portions thereof located on the 8th and 9th
floors of the Building shall not include or be deemed to include Area A-5 but
may include Area A-6 and Area A-7.

            7. The Lessee and the Port Authority each represents and warrants
that it has not had any contacts, dealings, acts or conversations with any
broker in connection with the negotiation or execution of this Supplemental
Agreement or in connection with the letting of the Additional Office Premises
hereunder except Insignia/ESG, Inc., a Delaware corporation having an office and
place of business at 200 Park Avenue, New York, New York 10166, and that there
is no broker with whom the Lessee or the Port Authority, as the case may be, has
dealt or had contacts or dealings or conversations with who is or may be
entitled to be paid a commission in connection with this Agreement and the
letting of the premises hereunder other than Insignia/ESG, Inc. The Lessee shall
indemnify and save harmless the Port Authority from and against any claims for
commission, brokerage or fees which have been or which may be made by any and
all persons, firms or corporations whatsoever for services in connection with
the negotiation and execution of this Agreement or in connection with the
letting of the premises hereunder arising out of the contacts, dealings, acts or
conversations of the Lessee, except for a claim of Insignia/ESG, Inc., if the
said claim is made in accordance with and pursuant to the terms of an agreement
between Insignia/ESG, Inc. and the Port Authority, dated December 31, 1998 (the
"Brokerage Agreement"), it being understood that the Additional Office Premises
are and constitute Additional Space included in the Lease pursuant to Section 44
of the Lease for the purposes of said Brokerage Agreement. The Port Authority
shall indemnify and save harmless the Lessee from and against any claims for
commission, brokerage or fees which have been or which may be made by any and
all persons, firms or corporations whatsoever for services in connection with
the negotiation and execution of this Supplemental Agreement or in connection
with the letting of the premises hereunder arising out of the contacts,
dealings, acts or conversations of the Port Authority including, without
limitation a claim of Insignia/ESG, Inc. if such claim is made in accordance
with and pursuant to the terms of the said Brokerage Agreement entered into
between the Port Authority and Insignia/ESG, Inc. dated December 31, 1998.

            8 Capitalized terms not defined in this Supplemental Agreement shall
have the meanings ascribed by such terms in the Lease.

            9. Neither the Commissioners of the Port Authority nor the directors
of the Lessee nor any of them, nor any officer, agent, member shareholder,
partner or employee of the


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Port Authority or of the Lessee shall be charged personally by any party hereto
with any liability or held liable to them under any term or provision of this
Agreement, or because of its execution or attempted execution or because of any
breach or attempted or alleged breach thereof.

            10. As hereby amended, all of the terms, covenants, provisions,
conditions and agreements of the Lease shall be and remain in full force and
effect.

            11. This Agreement and the Lease which it amends constitute the
entire agreement between the Port Authority and the Lessee on the subject
matter, and may not be changed, modified, discharged or extended except by
instrument in writing duly executed on behalf of both the Port Authority and the
Lessee. The Lessee agrees that no representations or warranties shall be binding
upon the Port Authority unless expressed in writing in the Lease or in this
Agreement.

            IN WITNESS WHEREOF, the Port Authority and the Lessee have executed
these presents, as of the day and year first above written.

ATTEST:                                 THE PORT AUTHORITY OF NEW YORK
                                                AND NEW JERSEY

/s/ Daniel D. [ILLEGIBLE]               By /s/ [ILLEGIBLE]
----------------------------------        --------------------------------------
Daniel D. [ILLEGIBLE]
Secretary                               (Title) DIRECTOR OF REAL ESTATE
The Port Authority of NY & NJ                   --------------------------------
                                                        (Seal)


ATTEST:                                 CREDIT SUISSE FIRST BOSTON
                                        CORPORATION

/s/ [ILLEGIBLE]                         By /s/ [ILLEGIBLE]
----------------------------------        --------------------------------------
Assistant Secretary

                                        (Title) Director
                                                --------------------------------
                                                      (Corporate Seal)


                                       8
<PAGE>

            (New York "All-Purpose" Acknowledgement - Port Authority)

STATE OF NEW YORK       )
                        )ss.:
COUNTY OF NEW YORK      )

      On the 30th day of August, 2000, before me, the undersigned, a Notary
Public in and for said State, personally appeared Cherrie [ILLEGIBLE], known to
me or proved to me on the basis of satisfactory evidence to be the individual
whose name is subscribed to the within instrument and acknowledged to me that
he/she signed the executed the same in his/her capacity, and that by his/her
signature on the instrument, the individual, or the person on behalf of which
the individual acted, executed the instrument.


                                                     /s/ Sylvia Shepherd

                                                         SYLVIA SHEPHERD
                                                Notary Public, State of New York
                                                          No. 41-4952176
                                                   Qualified in Queens County
                      (notarial seal and stamp) Commission Expires June 12, 2001

                  (New York "All-Purpose Acknowledgment - LLC)

STATE OF New York       )
                        )ss.:
COUNTY OF Richmond      )

      On the 24th day of August, 2000, before me, the undersigned, a Notary
Public in and for said State, personally appeared FRANK J. BARTOLOTTA, known to
me or proved to me on the basis of satisfactory evidence to be the individual
whose name is subscribed to the within instrument and acknowledged to me that
he/she signed the executed the same in his/her capacity, and that by his/her
signature on the instrument, the individual, or the person on behalf of which
the individual acted, executed the instrument.


                                            /s/ Ellen A McCool
                                                Ellen A McCool

      ELLEN A. McCOOL
Notary Public, State of New York
       No. 43-4948821                      (notarial seal and stamp)
  Qualified in Richmond County
  Commission Expires 3-27-2001


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