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                                                                   EXHIBIT 10.43
 
                                  GUARANTY
                                  --------


                                  RECITALS
                                  --------

     1.  On or about August 27, 1998, JAMES L. and NANCY J. BILDNER entered into
a written Promissory Note in favor of NATIONSBANK, N.A. in the principal sum of
TWO MILLION THREE HUNDRED AND TEN THOUSAND DOLLARS ($2,310,000.00).

     2.  Said Promissory Note was secured by:

         a.) A Deed of Trust dated August 27, 1998 on real property located at
scenic Road 6 SW of Ocean, Carmel, CA 93921 in which NATIONSBANK, N.A. is named
as the Beneficiary; and

         b.) A Pledge Agreement pledging certain shares of  Tier Technologies,
Inc., a California corporation held in Account No. 209-71082 at NationsBanc
Montgomery Securities, LLC, the fair market value of which is required to remain
in excess of $2,310,000.00.

     3.  In consideration of NATIONSBANK, N.A. terminating the Pledge Agreement
in number 2(b) above, including its Power of Sale clause, the undersigned
hereinafter called "Guarantor", in recognition of the importance of JAMES L.
BILDNER as a key employee of the Guarantor, agrees as follows:

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     FOR VALUABLE CONSIDERATION, Guarantor guarantees and promises to pay to
NATIONSBANK, N.A. (hereinafter called "Obligee"), on order or demand, in lawful
money of the United States, up to and including One Million Dollars ($1,000,000)
of the indebtedness of JAMES L. BILDNER and NANCY J. BILDNER (hereinafter called
collectively "Borrower"), arising or existing under that certain Promissory Note
dated AUGUST 27, 1998, a copy of which is attached hereto, marked Exhibit A and
by this reference made a part hereof as though set forth in full and that
certain Deed of Trust between JAMES L. BILDNER and Obligee dated AUGUST 27,
1998, (hereinafter collectively called the "Obligation"), a copy of which is
attached hereto, marked Exhibit B. Guarantor hereby acknowledges receipt of
unsigned copies of the Obligation to Obligee.

     The word "indebtedness" is used herein in its most comprehensive sense
subject to the limitation of liability of ONE MILLION DOLLARS ($1,000,000) and
whether recovery upon such indebtedness may be or hereafter become barred by
any statute or limitations, or whether such indebtedness may be or hereafter
become otherwise unenforceable.

     The Guarantor shall be entitled to a sixty (60) day period in which to cure
any default of Borrower.  During any

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such period, Guarantor shall have an unconditional right to cure any default.
Guarantor's payment of any sums in default, without regard to acceleration
provisions, shall cure any payment default and allow the note to continue in
effect as if no default had occurred.  However, Guarantor shall be limited in
its ability to cure defaults to a total number of five times over the life of
the loan and to no more than two times in any one year.  If a payment is made by
Guarantor on behalf of Borrower pursuant to the terms of the Promissory Note and
said payment is timely, it shall not be considered a default.  Additionally, any
payments made by Borrower or others on principal due and owing shall reduce the
guaranteed amount ($1,000,000) accordingly.  Notwithstanding the foregoing, once
the principal amount of the obligation is reduced to One Million Three Hundred
Ten Thousand Dollars ($1,310,000), this Guaranty shall be automatically
revoked.

     The obligations hereunder are joint and several, and independent of the
obligations of Borrower, and a separate action or actions may be brought and
prosecuted against Guarantor whether action is brought against Borrower or
whether Borrower is joined in any such action or actions; and

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Guarantor waives the benefit of any statute of limitations affecting its
liability hereunder or the enforcement thereof.

     1.  INDEMNITY.  In addition to the payment of expenses pursuant to
         ---------                                                     
Paragraph entitled "Expenses" on Page 6, Guarantor agrees to indemnify,
defend, exonerate, pay and hold Obligee and the officers, directors, employees
and agents of Obligee (the "Indemnitees") harmless from and against any and
all liabilities, obligations, losses, damages, penalties, actions, causes of
action, judgments, suits, claims, costs, expenses and disbursements of any
kind or nature whatsoever (including, without limitation, the fees and
disbursements of counsel to Obligee and reasonable expert witness fees and
disbursements) for such Indemnitees in Connection with any investigative,
administrative or judicial proceeding, whether or not such Indemnitee shall be
designated a party thereto, that may be imposed on, incurred by or asserted
against such Indemnitee, in any manner relating to or arising out of or in
connection with this Guaranty (the "Indemnified Liabilities"). Notwithstanding
the foregoing, Indemnified Liabilities shall not include liabilities,
obligations, losses, damages, penalties, actions, causes of action, judgments,
suits, claims, costs, expenses and disbursements to the extent caused by or

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resulting from the gross negligence or willful misconduct of such Indemnitee.

     2.  NOTICE.  Each Indemnitee will promptly notify Guarantor of each event
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of which it has knowledge that may give rise to a claim under section 1.

     3.  DEFENSE OF ACTIONS. If any investigative, judicial or administrative
         ------------------                                                  
proceeding arising in connection with any of the Indemnified Liabilities is
brought against any Indemnitee indemnified or intended to be indemnified
pursuant to Section 1, Guarantor, to the extent and in the manner directed by
the Indemnitee or intended Indemnitee, will resist and defend such action,
suit or proceeding or cause the same to be resisted and defended by counsel
designated by Indemnitees (which counsel shall be satisfactory to the
Guarantor). Each Indemnitee will use its best efforts to cooperate in the
defense of any such action, suit or proceeding. To the extent that the
undertaking to indemnify, pay and hold harmless set forth in the preceding
sentence may be unenforceable because it is violative of any law or public
policy, Guarantor shall make the maximum contribution to the payment and
satisfaction of each of the Indemnified Liabilities that is permissible under
applicable law.

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     4.  CONSENTS BY GUARANTOR.  Guarantor authorizes Obligee, without notice or
         ---------------------                                                  
demand and without affecting its liability hereunder, from time to time to (a)
renew, compromise, extend, accelerate (acceleration shall be subject to
Guarantor's right to cure a default as set forth on page 3 above) or otherwise
change the time for payment of, or otherwise change the terms of the
indebtedness or any part thereof, including increase or decrease of the rate of
interest therein; (b) take and hold security for the payment of the indebtedness
guaranteed, and exchange, enforce, waive and release any such security; (c)
apply such security and direct the order or manner of sale thereof as Obligee in
its discretion may determine; and (d) release or substitute any one or more of
the endorsers or guarantors.  Obligee may without notice assign this Guaranty in
whole or in part.

     Guarantor waives any right to require Obligee to (a) proceed against
Borrower; (b) proceed against or exhaust any security held from Borrower; or (c)
pursue any other remedy in Obligee's power whatsoever.  Guarantor waives any
defense arising by reason of the cessation from any cause whatsoever of the
liability of Borrower.  Until all indebtedness of Borrower to Obligee shall have
been paid in full, Guarantor shall have no right of subrogation, and waives any
right to

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enforce any remedy which Obligee now has or may hereafter have against Borrower,
and waives any benefit of, and any right to participate in any security now or
hereafter held by Obligee.  Guarantor waives all presentments, demands for
performance, notices and non-performance, protests, notices of protest, notices
of dishonor, and notices of acceptance of this Guaranty and of the existence,
creation, or incurring of new or additional indebtedness.

     5.  WAIVER OF DEFENSES OF CALIFORNIA CODE OF CIVIL PROCEDURE  
         --------------------------------------------------------

SECTION 580(d).  GUARANTOR SHALL BE LIABLE TO OBLIGEE FOR ANY DEFICIENCY
--------------                                                          
RESULTING FROM THE EXERCISE BY IT OF ANY SUCH REMEDY, EVEN THOUGH ANY RIGHTS
WHICH GUARANTOR MAY HAVE AGAINST OTHERS MIGHT BE DESTROYED.  GUARANTOR
UNDERSTANDS THAT IF OBLIGEE SELECTS NON-JUDICIAL FORECLOSURE, IT WILL HAVE A
DEFENSE TO A DEFICIENCY JUDGMENT AND IT IS THAT DEFENSE WHICH THE GUARANTOR
SPECIFICALLY HEREBY WAIVES.  GUARANTOR SPECIFICALLY WAIVES THE "GRADSKY DEFENSE"
AND ANY OTHER DEFENSES IT MAY BE ENTITLED TO PURSUANT TO CALIFORNIA CODE OF
                                                                    -------
CIVIL PROCEDURE SECTIONS 580a, 580b, 580d AND 726. GUARANTOR WAIVES ANY RIGHT TO
---------------                                                                 
REQUIRE OBLIGEE TO (A) PROCEED AGAINST BORROWER; (B) PROCEED AGAINST OR EXHAUST
ANY SECURITY HELD FROM BORROWER; OR (C) PURSUE ANY OTHER REMEDY IN OBLIGEE'S
POWER WHATSOEVER.

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     GUARANTOR, PURSUANT TO CALIFORNIA CIVIL CODE SECTION 2856,
                                       ----------

". . . WAIVES ALL RIGHTS AND DEFENSES THAT THE GUARANTOR MAY HAVE BECAUSE THE
DEBTOR'S DEBT IS SECURED BY REAL PROPERTY.  THIS MEANS, AMONG OTHER THINGS:

     (1) THE CREDITOR MAY COLLECT FROM THE GUARANTOR WITHOUT FIRST FORECLOSING
ON ANY REAL OR PERSONAL PROPERTY COLLATERAL PLEDGED BY THE DEBTOR.

     (2) IF THE CREDITOR FORECLOSES ON ANY REAL PROPERTY COLLATERAL PLEDGED BY
THE DEBTOR:

     (A) THE AMOUNT OF THE DEBT MAY BE REDUCED ONLY BY THE PRICE FOR WHICH
THAT COLLATERAL IS SOLD AT THE FORECLOSURE SALE, EVEN IF THE COLLATERAL IS
WORTH MORE THAN THE SALE PRICE.

     (B) THE CREDITOR MAY COLLECT FROM THE GUARANTOR EVEN IF THE CREDITOR, BY
FORECLOSING ON THE REAL PROPERTY COLLATERAL, HAS DESTROYED ANY RIGHT THE
GUARANTOR MAY HAVE TO COLLECT FROM THE DEBTOR.

     THIS IS AN UNCONDITIONAL AND IRREVOCABLE WAIVER OF ANY RIGHTS AND
DEFENSES THE GUARANTOR MAY HAVE BECAUSE THE DEBTOR'S DEBT IS SECURED BY REAL
PROPERTY. THESE RIGHTS AND DEFENSES INCLUDE, BUT ARE NOT LIMITED TO, ANY
RIGHTS OR DEFENSES BASED UPON SECTION 580a, 580b, 580d, OR 726 OF THE CODE OF
                                                                      -------
CIVIL PROCEDURE.
---------------

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     (C) WITHOUT LIMITING ANY RIGHTS OF THE CREDITOR OR ANY GUARANTOR OR OTHER
SURETY TO USE ANY OTHER LANGUAGE TO EXPRESS AN INTENT TO WAIVE ALL RIGHTS AND
DEFENSES OF THE SURETY BY REASON OF ANY ELECTION OF REMEDIES BY THE CREDITOR,
THE FOLLOWING PROVISION SHALL BE EFFECTIVE TO WAIVE ALL RIGHTS AND DEFENSES
THE GUARANTOR OR OTHER SURETY MAY HAVE IN RESPECT OF HIS OR HER OBLIGATIONS AS
A SURETY BY REASON OF AN ELECTION OF REMEDIES BY THE CREDITOR:

     THE GUARANTOR WAIVES ALL RIGHTS AND DEFENSES ARISING OUT OF AN ELECTION
OF REMEDIES BY THE CREDITOR, EVEN THOUGH THAT ELECTION OF REMEDIES, SUCH AS A
NON-JUDICIAL FORECLOSURE WITH RESPECT TO SECURITY FOR A GUARANTEED OBLIGATION,
HAS DESTROYED THE GUARANTOR'S RIGHTS OF SUBROGATION AND REIMBURSEMENT AGAINST
THE PRINCIPAL BY THE OPERATION OF SECTION 580d OF THE CODE OF CIVIL PROCEDURE
                                                      -----------------------
OR OTHERWISE."

     6.  EXPENSES. Guarantor agrees to pay all attorneys' fees and all other
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costs and out-of-pocket expenses which may be incurred by Obligee in the
enforcement or collection of this Guaranty and the Guaranteed Obligation,
whether or not suit is filed.

     7.  INTEREST. All amounts required to be paid to Obligee by Guarantor
         --------                                                         
pursuant to the provisions of this Guaranty shall bear interest from and
including the date

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upon which such amounts are due, to and excluding the date of payment thereof,
at the rate of ten (10%) percent per annum.  All payments of such amounts by
Guarantor shall include any such accrued interest.

     8.  HEADINGS.  The Section and other headings contained in this Guaranty
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are for reference purposes only and shall not affect in any way the meaning or
interpretation of this Guaranty.

     9.  GOVERNING LAW.  The validity, construction and performance of this
         -------------                                                     
Guaranty shall be governed by the laws, without regard to the laws as to choice
or conflict of laws, of the State of California.

     10.  ENTIRE AGREEMENT.  This Guaranty embodies the entire agreement and
          ----------------                                                  
understanding between the parties pertaining to the subject matter of this
Guaranty, and supersedes all prior agreements, understandings, negotiations,
representations and discussions, whether verbal or written, of the parties,
pertaining to that subject matter.

     11.  ASSIGNMENT. Neither this Guaranty nor any rights under this Guaranty
          ----------                                                          
may be assigned by Guarantor without the prior written consent of Obligee.

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     12.  BINDING EFFECT. The provisions of this Guaranty shall bind and inure
          --------------                                                      
to the benefit of the parties hereto and their respective successors and
permitted assigns.

     13.  PARTIES IN INTEREST. Nothing in this Guaranty, expressed or implied,
          -------------------                                                 
is intended to confer on any person or entity other than the parties any right
or remedy under or by reason of this Guaranty.

     14.  NOTICES.  Any notice or communication required or permitted by this
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guaranty shall be deemed sufficiently given in writing and, if delivered
personally, when it is delivered or if deposited with the U.S. Postal Service,
postage prepaid, and addressed to the party to receive it at the address set
forth below 48 hours after such deposit as registered or certified mail.

 
 
        To Obligee:                     NationsBank, N.A.   
                                        Attention: Frank Drury            
                                        600 Montgomery St., 37th Fl.           
                                        San Francisco, CA 94111            

        With copy to:                   Peter A. Hass, Esq.  
                                        Watson, Hoffe & Hass                 
                                        3700 Barrett Avenue                 
                                        P. 0. Box 5001                    
                                        Richmond, CA 94805-2297                
        
        To Guarantor:                   Bruce Deming, Esq.   
                                        Tier Technologies, Inc.             
                                        1350 Treat Blvd., Ste. 250             
                                        Walnut Creek, CA 94596               
                                                     
        To Borrower:                    James L. and Nancy J. Bildner
                                        5 Boardman Avenue                  
                                        Manchester, MA 01944                  

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     15.  AMENDMENT AND WAIVER.  This Guaranty may be amended, modified or
          --------------------                                            
supplemented only by a writing executed by each of the parties.  Any party may
in writing waive any provisions of this Guaranty to the extent such provision is
for the benefit of the waiving party.  No action taken pursuant to this
Guaranty, including any investigation by or on behalf of any party, shall be
deemed to constitute a waiver by that party of its or any other party's
compliance with any representations or warranties or with any provisions of this
Guaranty.  No waiver by any party of a breach of any provision of this Guaranty
shall be construed as a waiver of any subsequent or different breach, and no
forbearance by a party to seek a remedy for noncompliance or breach by another
party shall be construed as a waiver of any right or remedy with respect to such
noncompliance or breach.

     16.  VENUE, JURISDICTION AND PROCESS. The parties agree that any suit,
          -------------------------------                                  
action or proceeding arising out of or relating to this Guaranty, or the
interpretation, performance (or breach of this Guaranty, shall be instituted in
any court of the State of California located in Monterey County, and each party
irrevocably submits to the jurisdiction of those courts and waives any and all
objections to jurisdiction or

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venue that it may have under the laws of the State of California or otherwise in
those courts in any such suit, action or proceeding.

     17.  PROMPT ACTION.  Time is of the essence with respect to each provision
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of this Guaranty.

     18.  SEVERABILITY. The invalidity or unenforceability of any particular
          ------------                                                      
provision of this Guaranty shall not affect the other provisions, and this
Guaranty shall be construed in all respects as if any invalid or unenforceable
provision were omitted.

     19.  FURTHER ACTION.  Each party agrees to perform any further acts and to
          --------------                                                       
execute and deliver any other documents which may be reasonably necessary to
effect the provisions of this Guaranty.

     20.  SURVIVAL OF REPRESENTATIONS AND WARRANTIES.  All representations and
          ------------------------------------------                          
warranties of guarantor contained in this Guaranty shall survive the execution
and delivery of this Guaranty and shall continue until any and all Guaranteed

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Obligation has been fully paid, performed and discharged in full.

     IN WITNESS WHEREOF, the undersigned Guarantor has executed this Guaranty
this 22 day of December, 1998.


GUARANTOR:


TIER TECHNOLOGIES, INC.,
a California corporation


BY:   /s/ James L. Bildner                       BY:   /s/ George K. Ross 
      --------------------------                       --------------------
      JAMES L. BILDNER, CHAIRMAN                       GEORGE K. ROSS, EXEC.
      OF THE BOARD AND CHIEF                           VICE PRESIDENT AND
      EXECUTIVE OFFICER                                CHIEF FIN. OFFICER

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