<PAGE>   1
                                                                      EXHIBIT 20

                                  [FIRST LOGO]

                                PROMISSORY NOTE

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<S>                 <C>              <C>             <C>        <C>         <C>       <C>       <C>
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  PRINCIPAL          LOAN DATE        MATURITY       LOAN NO    CALL/COLL   ACCOUNT   OFFICER   INITIALS
$1,000,050.00        03-06-2001      04-01-2002       655028     4A/20                  RCB
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          References in the shaded area are for Lender's use only and do not limit the
       applicability of this document to any particular loan or item. Any item above
              containing "***" has been omitted due to text length limitations.

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</TABLE>

<TABLE>
<S>                                                    <C>
BORROWER: WESTECH CAPITAL CORP. (TIN: 13-3577716)      LENDER: FIRST UNITED BANK
          2700 VIA FORTUNE SUITE 400                           LUBBOCK SOUTHWEST BRANCH
          AUSTIN, TX 78746                                     6604 FRANKFORD
                                                               LUBBOCK, TX 79424
</TABLE>

<TABLE>
<S>                                    <C>                       <C>
PRINCIPAL AMOUNT: $1,000,050.00       INITIAL RATE: 9.500%       DATE OF NOTE: MARCH 6, 2001
</TABLE>

PROMISE TO PAY. WESTECH CAPITAL CORP. ("BORROWER") PROMISES TO PAY TO FIRST
UNITED BANK ("LENDER"), OR ORDER, IN LAWFUL MONEY OF THE UNITED STATES OF
AMERICA, THE PRINCIPAL AMOUNT OF ONE MILLION FIFTY & 00/100 DOLLARS
($1,000,050.00), TOGETHER WITH INTEREST ON THE UNPAID PRINCIPAL BALANCE FROM
MARCH 6, 2001, UNTIL MATURITY. THE INTEREST RATE WILL NOT INCREASE ABOVE
18.000%.

PAYMENT. SUBJECT TO ANY PAYMENT CHANGES RESULTING FROM CHANGES IN THE INDEX,
BORROWER WILL PAY THIS LOAN ON DEMAND. PAYMENT IN FULL IS DUE IMMEDIATELY UPON
LENDER'S DEMAND. IF NO DEMAND IS MADE, BORROWER WILL PAY THIS LOAN IN 12
PRINCIPAL PAYMENTS OF $50,000.00 EACH AND ONE FINAL PRINCIPAL AND INTEREST
PAYMENT OF $403,322.63. BORROWER'S FIRST PRINCIPAL PAYMENT IS DUE APRIL 1,
2001, AND ALL SUBSEQUENT PRINCIPAL PAYMENTS ARE DUE ON THE SAME DAY OF EACH
MONTH AFTER THAT. IN ADDITION, BORROWER WILL PAY REGULAR MONTHLY PAYMENTS OF
ALL ACCRUED UNPAID INTEREST DUE AS OF EACH PAYMENT DATE, BEGINNING APRIL 1,
2001, WITH ALL SUBSEQUENT INTEREST PAYMENTS TO BE DUE ON THE SAME DAY OF EACH
MONTH AFTER THAT. BORROWER'S FINAL PAYMENT DUE APRIL 1, 2002, WILL BE FOR ALL
PRINCIPAL AND ALL ACCRUED INTEREST NOT YET PAID. UNLESS OTHERWISE AGREED OR
REQUIRED BY APPLICABLE LAW, PAYMENTS WILL BE APPLIED FIRST TO ACCRUED UNPAID
INTEREST, THEN TO PRINCIPAL, AND ANY REMAINING AMOUNT TO ANY UNPAID COLLECTION
COSTS. THE ANNUAL INTEREST RATE FOR THIS NOTE IS COMPUTED ON A 365/360 BASIS;
THAT IS, BY APPLYING THE RATIO OF THE ANNUAL INTEREST RATE OVER A YEAR OF 360
DAYS, MULTIPLIED BY THE OUTSTANDING PRINCIPAL BALANCE, MULTIPLIED BY THE ACTUAL
NUMBER OF DAYS THE PRINCIPAL BALANCE IS OUTSTANDING, UNLESS SUCH CALCULATION
WOULD RESULT IN A USURIOUS RATE, IN WHICH CASE INTEREST SHALL BE CALCULATED ON
A PER DIEM BASIS OF A YEAR OF 365 OR 366 DAYS, AS THE CASE MAY BE. Borrower
will pay Lender at Lender's address shown above or at such other place as
Lender may designate in writing. Notwithstanding any other provision of this
Note, Lender will not charge interest on any undisbursed loan proceeds. No
scheduled payment, whether of principal or interest or both, will be due unless
sufficient loan funds have been disbursed by the scheduled payment date to
justify the payment.

AMOUNT FINANCED. The Amount Financed under this Note is $1,000,000.00.

VARIABLE INTEREST RATE. The interest rate on this Note is subject to change
from time to time based on changes in an independent index which is the Wall
Street Journal Prime Rate (the "Index"). The index is not necessarily the
lowest rate charged by Lender on its loans. If the index becomes unavailable
during the term of this loan, Lender may designate a substitute index after
notice to Borrower. Lender will tell Borrower the current index rate upon
Borrower's request. The interest rate change will not occur more often than
each Day. Borrower understands that Lender may make loans based on other rates
as well. THE INDEX CURRENTLY IS 8.500% PER ANNUM. THE INTEREST RATE TO BE
APPLIED PRIOR TO MATURITY TO THE UNPAID PRINCIPAL BALANCE OF THIS NOTE WILL BE
AT A RATE OF 1.000 PERCENTAGE POINT OVER THE INDEX, RESULTING IN AN INITIAL
RATE OF 9.500% PER ANNUM. NOTWITHSTANDING THE FOREGOING, THE VARIABLE INTEREST
RATE OR RATES PROVIDED FOR IN THIS NOTE WILL BE SUBJECT TO THE FOLLOWING
MAXIMUM RATE. NOTICE: Under no circumstances will the interest rate on this
Note be more than the lesser of 18.000% per annum or the maximum rate allowed
by applicable law. for purposes of this Note, the "maximum rate allowed by
applicable law" means the greater of (A) the maximum rate of interest permitted
under federal or other law applicable to the indebtedness evidenced by this
Note, or (B)

PREPAYMENT. Borrower agrees that all loan fees and other prepaid finance
charges are earned fully as of the date of the loan and will not be subject to
refund upon early payment (whether voluntary or as a result of default), except
as otherwise required by law. Except for the foregoing, Borrower may prepay
this Note in part or in full at any time before final maturity, whether by
cash, a new loan, renewal, or otherwise. Prepayment in full shall consist of
payment of the remaining unpaid principal balance together with all accrued and
unpaid interest and all other amounts, costs and expenses for which Borrower is
responsible under this Note or any other agreement with Lender pertaining to
this loan, and in no event will Borrower ever be required to pay any unearned
interest. Early payments will not, unless agreed to by Lender in writing,
relieve Borrower of Borrower's obligation to continue to make payments under
the payment schedule. Rather, early payments will reduce the principal balance
due and may result in Borrower's making fewer payments. Borrower agrees not to
send Lender payments marked "paid in full", "without recourse", or similar
language. If Borrower sends such a payment, Lender may accept it without losing
any of Lender's rights under this Note, and Borrower will remain obligated to
pay any further amount owed to Lender. All written communications concerning
disputed amounts, including any check or other payment instrument that
indicates that the payment constitutes "payment in full" of the amount owed or
that is tendered with other conditions or limitations or as full satisfaction
of a disputed amount must be mailed or delivered to: First United Bank, Lubbock
Southwest Branch, 6604 Frankford, Lubbock, TX 79424.

INTEREST AFTER DEFAULT. Upon default, including failure to pay upon final
maturity, the total sum due under this Note will bear interest from the date of
acceleration or maturity at the variable interest rate on this Note. The
interest rate will not exceed the maximum rate permitted by applicable law.

DEFAULT. Each of the following shall constitute an event of default ("Event of
Default") under this Note:

     PAYMENT DEFAULT. Borrower fails to make any payment when due under this
     Note.

     OTHER DEFAULTS. Borrower fails to comply with or to perform any other term,
     obligation, covenant or condition contained in this Note or in any of the
     related documents or to comply with or to perform any term, obligation,
     covenant or condition contained in any other agreement between Lender and
     Borrower.

     FALSE STATEMENTS. Any warranty, representation or statement made or
     furnished to Lender by Borrower or on Borrower's behalf under this Note or
     the related documents is false or misleading in any material respect,
     either now or at the time made or furnished or becomes false or misleading
     at any time thereafter.

     INSOLVENCY. The dissolution or termination of Borrower's existence as a
     going business, the insolvency of Borrower, the appointment of a receiver
     for any part of Borrower's property, any assignment for the benefit of
     creditors, any type of creditor workout, or the commencement of any
     proceeding under any bankruptcy or insolvency laws by or against Borrower.

     CREDITOR OR FORFEITURE PROCEEDINGS. Commencement of foreclosure or
     forfeiture proceedings, whether by judicial proceeding, self-help,
     repossession or any other method, by any creditor of Borrower or by any
     governmental agency against any collateral securing the loan. This includes
     a garnishment of any of Borrower's accounts, including deposit accounts,
     with Lender. However, this Event of Default shall not apply if there is a
     good faith dispute by Borrower as to the validity or reasonableness of the
     claim which is the basis of the creditor or forfeiture proceeding and if
     Borrower gives Lender written notice of the creditor or forfeiture
     proceeding and deposits with Lender monies or a surety bond for the
     creditor or forfeiture proceeding, in an amount determined by Lender, in
     its sole discretion, as being an adequate reserve or bond for the dispute.

     EVENTS AFFECTING GUARANTOR. Any of the preceding events occurs with respect
     to any Guarantor of any of the indebtedness or any Guarantor dies or
     becomes incompetent, or revokes or disputes the validity of, or liability
     under, any guaranty of the indebtedness evidenced by this Note. In the
     event of a death, Lender, at its option, may, but shall not be required to,
     permit the Guarantor's estate to assume unconditionally the obligations
     arising under the guaranty in a manner satisfactory to Lender, and, in
     doing so, cure any Event of Default.

     CHANGE IN OWNERSHIP. Any change in ownership of twenty-five percent (25%)
     or more of the common stock of Borrower.

     ADVERSE CHANGE. A material adverse change occurs in Borrower's financial
     condition, or Lender believes the prospect of payment or performance of
     this Note is impaired.

     INSECURITY. Lender in good faith believes itself insecure.

     CURE PROVISIONS. If any default, other than a default in payment or failure
     to satisfy Lender's requirement in the Insufficient Market Value of
     Securities section is curable, it may be cured (and no event of default
     will have occurred) if Borrower, after receiving written notice from Lender
     demanding cure of such default: (1) cures the default within twenty (20)
     days; or (2) if the cure requires more than twenty (20) days, immediately
     initials steps which Lender deems in Lender's sole discretion to be
     sufficient to cure the default and thereafter continues and completes all
     reasonable and necessary steps sufficient to produce compliance as soon as
     reasonably practical.

LENDER'S RIGHTS. Upon default, Lender may declare the entire indebtedness,
including the unpaid principal balance on this Note, all accrued

<PAGE>   2
                                PROMISSORY NOTE
LOAN NO. 655028                   (CONTINUED)                             PAGE 2
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unpaid interest, and all other amounts, costs and expenses for which Borrower is
responsible under this Note or any other agreement with Lender pertaining to
this loan, immediately due, without notice, and then Borrower will pay that
amount.

ATTORNEYS' FEES; EXPENSES. Lender may hire an attorney to help collect this
Note if Borrower does not pay, and Borrower will pay Lender's reasonable
attorneys' fees. Borrower also will pay Lender all other amounts Lender
actually incurs as court costs, lawful fees for filing, recording, releasing to
any public office any instrument securing this Note; the reasonable cost
actually expended for repossessing, storing, preparing for sale, and selling
any security; and fees for noting a lien on or transferring a certificate of
title to any motor vehicle offered as security for this Note, or premiums or
indentifiable charges received in connection with the sale of authorized
insurance.

GOVERNING LAW. THIS NOTE WILL BE GOVERNED BY, CONSTRUED AND ENFORCED IN
ACCORDANCE WITH FEDERAL LAW AND THE LAWS OF THE STATE OF TEXAS. THIS NOTE HAS
BEEN ACCEPTED BY LENDER IN THE STATE OF TEXAS.

CHOICE OF VENUE. If there is a lawsuit, and if the transaction evidenced by
this Note occurred in Lubbock County, Borrower agrees upon Lender's request to
submit to the jurisdiction of the courts of Lubbock County, State of Texas.

RIGHT OF SETOFF. To the extent permitted by applicable law, Lender reserves a
right of setoff in all Borrower's accounts with Lender (whether checking,
savings, or some other account). This includes all accounts Borrower holds
jointly with someone else and all accounts Borrower may open in the future.
However, this does not include any IRA of Keogh accounts, or any trust accounts
for which setoff would be prohibited by law. Borrower authorizes Lender, to the
extent permitted by applicable law, to charge or setoff all sums owing on the
indebtedness against any and all such accounts.

COLLATERAL. Borrower acknowledges this Note is secured by A SECURITY AGREEMENT
FROM WESTECH CAPITAL CORP., A NEW YORK CORPORATION AND TEJAS SECURITIES GROUP,
INC., A TEXAS CORPORATION TO FIRST UNITED BANK DATED 06/07/00 AND A PLEDGE AND
SECURITY AGREEMENT FROM TEJAS SECURITIES GROUP HOLDING COMPANY TO FIRST UNITED
BANK DATED 06/07/00.

PRIOR NOTE. RENEWAL OF NOTE #655028.

SUCCESSOR INTERESTS. The terms of this Note shall be binding upon Borrower, and
upon Borrower's heirs, personal representatives, successors and assigns, and
shall inure to the benefit of Lender and its successors and assigns.

GENERAL PROVISIONS. This Note is payable on demand. The inclusion of specific
default provisions or rights of Lender shall not preclude Lender's right to
declare payment of this Note on its demand. If any part of this Note cannot be
enforced, this fact will not affect the rest of the Note. Borrower does not
agree or intend to pay, and Lender does not agree or intend to contract for,
charge, collect, take, reserve or receive (collectively referred to herein as
"charge or collect"), any amount in the nature of interest or in the nature of
a fee for this loan, which would in any way or event (including demand,
prepayment, or acceleration) cause Lender to charge or collect more for this
loan than the maximum Lender would be permitted to charge or collect by federal
law or the law of the State of Texas (as applicable). Any such excess interest
or unauthorized fee shall, instead of anything stated to the contrary, be
applied first to reduce the principal balance of this loan, and when the
principal has been paid in full, be refunded to Borrower. The right to
accelerate maturity of sums due under this Note does not include the right to
accelerate any interest which has not otherwise accrued on the date of such
acceleration, and Lender does not intend to charge or collect any unearned
interest in the event of acceleration. All sums paid or agreed to be paid to
Lender for the use, forbearance or detention of sums due hereunder shall, to
the extent permitted by applicable law, be amortized, prorated, allocated and
spread throughout the full term of the loan evidenced by this Note until
payment in full so that the rate or amount of interest on account of the loan
evidenced hereby does not exceed the applicable usury ceiling. Lender may delay
or forgo enforcing any of its rights or remedies under this Note without losing
them. Borrower and any other person who signs, guarantees or endorses this
Note, to the extent allowed by law, waive presentment, demand for payment,
notice of dishonor, notice of intent to accelerate the maturity of this Note,
and notice of acceleration of the maturity of this Note. Notwithstanding any
other provision of this Note, Borrower does not waive any right accruing to
Borrower under the provisions of the Texas Finance Code. Upon any change in the
terms of this Note, and unless otherwise expressly stated in writing, no party
who signs this Note, whether as maker, guarantor, accommodation maker or
endorser, shall be released from liability. The obligations under this Note are
joint and several.

PRIOR TO SIGNING THIS NOTE, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS OF
THIS NOTE, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS. BORROWER AGREES TO
THE TERMS OF THE NOTE.

BORROWER ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THIS PROMISSORY NOTE.

BORROWER:


WESTECH CAPITAL CORP.

BY: /s/ JOHN GORMAN
    --------------------------------------
    JOHN GORMAN, CHAIRMAN & CEO OF WESTECH
    CAPITAL CORP.


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