<PAGE>

                                                                   Exhibit 10.25

                           FIFTH AMENDMENT TO LEASE

     THIS FIFTH AMENDMENT TO LEASE (this "Amendment") is entered into as of the
12th day of December, 2000, by and between THE PRUDENTIAL INSURANCE COMPANY OF
AMERICA, a New Jersey corporation ("Landlord") and VIGNETTE CORPORATION, a
Delaware corporation ("Tenant").

     WHEREAS, B.O. III, Ltd., a Texas limited partnership and Tenant executed
that certain Office Lease Agreement (the "Lease Agreement") dated August 4, 1998
covering 66,900 square feet of Agreed Rentable Area in the building known as
Barton Oaks Plaza III (the "Building"), as more particularly described therein;

     WHEREAS, the Lease Agreement has been amended pursuant to that certain
First Amendment to Lease dated as of October 31, 1998, that certain Second
Amendment to Lease dated as of December 30, 1998, that certain Third Amendment
to Lease dated as of April 27, 1999, and that certain Fourth Amendment to Lease
dated August 1, 2000 (the Lease Agreement, as amended, the "Lease");

     WHEREAS, Landlord is the current owner of the Building and the landlord
under the Lease;

     WHEREAS, Tenant is the sublessee under that certain Sublease dated
September 21, 1999 by and between IXC Communications Services, Inc. ("IXC") and
Tenant (the "Sublease") covering 24,134 square feet of Agreed Rentable Area on
the second floor of the Building shown on Exhibit A attached hereto ("Second
                                          ---------
Floor Premises");

     WHEREAS, IXC's lease and the Sublease terminate on January 31, 2002;

     WHEREAS, pursuant to Rider 5 to the Lease, Tenant has a right of
opportunity to lease the Second Floor Premises upon the termination of IXC's
lease; and

     WHEREAS, Tenant has exercised its right of opportunity to lease the Second
Floor Premises and Landlord and Tenant desire to amend the Lease to reflect
their agreements as to the terms and conditions governing Tenant's lease of the
Second Floor Premises.

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
between the parties herein contained, Landlord and Tenant hereby agree as
follows:

1.   Premises.  Effective as of February 1, 2002, Item 2 of the Basic Lease
     --------
Provisions shall be amended in its entirety to read as follows:

     Premises:

     a.   Suite #: 500 ; Floors: A portion of the first (1/st/) floor and the
          entire fourth (4/th/) and fifth (5/th/) floors (the "Original
          Premises"); the remaining 5,049 square feet of Agreed Rentable Area on
          the first (1/st/) floor (the "First Floor Expansion Premises"), 12,009
          square feet of Agreed Rentable Area on the third (3/rd/) floor (the
          "Third Floor Expansion Premises") (the First Floor Expansion Premises
          and the Third Floor Expansion Premises, collectively, the "Expansion
          Premises"); 24,134 square feet of Agreed Rentable Area on the Second
          Floor (the "Second Floor Premises") and 13,331 square feet of Agreed
          Rentable Area on the third (3/rd/) floor (the "Third Floor Right of
          First Refusal Premises").

                                       1
<PAGE>

     b.  Agreed Rentable Area: 121,423 square feet.

2.   Basic Rent.  Effective February 1, 2002, Item 3.a of the Basic Lease
     ----------
Provisions shall be amended by adding the following at the end of such item:

          With respect to the Second Floor Premises:

                              Rate Per Square   Basic        Basic
          Rental              Foot of Agreed    Annual       Monthly
          Period              Rentable Area     Rent         Rent
          ------              --------------    ----         ----

          2/1/02 - 1/31/06    $23.00            $555,081.96  $46,256.83


3.   Tenant's Pro Rata Share Percentage.  Item 4.a of the Basic Lease Provisions
     ----------------------------------
shall be amended as follows:

     (a)  Effective February 1, 2002, Item 4.a of the Basic Lease Provisions
          shall be amended in its entirety to read as follows:

          a.   Tenant's Pro Rata Share Percentage: 100.00% (the Agreed Rentable
               Area of the Premises divided by the Agreed Rentable Area of the
               Building, expressed in a percentage).

     (b)  Effective June 1, 2003, Item 4.a of the Basic Lease Provisions shall
          be amended as follows:

          (i)  In the event Tenant exercises its right to renew the Lease with
     respect to the Third Floor Right of First Refusal Premises, Item 4.a shall
     not be amended.

          (ii) In the event Tenant does not exercise its right to renew the
     Lease with respect to the Third Floor Right of First Refusal Premises, Item
     4.a shall be amended in its entirety to read as follows:

          a.   Tenant's Pro Rata Share Percentage: 89.021% (the Agreed Rentable
               Area of the Premises divided by the Agreed Rentable Area of the
               Building, expressed in a percentage).

     (c)  Effective December 3, 2003, Item 4.a of the Basic Lease Provisions
shall be amended as follows:

          (i)  In the event Tenant exercises its right to renew the Lease with
     respect to the Original Premises and the Expansion Premises and has
     exercised its right to renew the Lease with respect to the Third Floor
     Right of First Refusal Premises, Item 4.a shall not be amended.

          (ii) In the event Tenant exercises its right to renew the Lease with
     respect to the Original Premises and the Expansion Premises, but has not
     exercised its right to renew the Lease with respect to the Third Floor
     Right of First Refusal Premises, Item 4.a shall not be amended.

                                       2
<PAGE>

          (iii)  In the event Tenant does not exercise its right to renew the
     Lease with respect to the Original Premises and the Expansion Premises, but
     has exercised its right to renew the Lease with respect to the Third Floor
     Right of First Refusal Premises, Item 4.a shall be amended in its entirety
     to read as follows:

          a.     Tenant's Pro Rata Share Percentage: 30.855% (the Agreed
                 Rentable Area of the Premises divided by the Agreed Rentable
                 Area of the Building, expressed in a percentage).

          (iv)   In the event Tenant does not exercise its right to renew the
     Lease with respect to the Original Premises and the Expansion Premises and
     has not exercised its right to renew the Lease with respect to the Third
     Floor Right of First Refusal Premises, Item 4.a shall be amended in its
     entirety to read as follows:

          a.     Tenant's Pro Rata Share Percentage: 19.876% (the Agreed
                 Rentable Area of the Premises divided by the Agreed Rentable
                 Area of the Building, expressed in a percentage).

     (d)  Effective February 1, 2006, Tenant's Pro Rata Share Percentage shall
be amended to reflect the percentage obtained by dividing the Agreed Rentable
Area of the Premises, if any, by the Agreed Rentable Area of the Building.

4.   Term.  Effective February 1, 2002, Item 5 of the Basic Lease Provisions
     ----
shall be amended in its entirety to read as follows:

     a.   With respect to the Original Premises and the Expansion Premises, Five
          (5) years and Zero (0) months (see Article 1, Supplemental Lease
          Provisions).

     b.   With respect to the Second Floor Premises, Four (4) years and Zero (0)
          months (see Article 1, Supplemental Lease Provisions).

     c.   With respect to the Third Floor Right of First Refusal Premises, Three
          (3) years and eleven (11) months (see Article 1, Supplemental Lease
          Provisions).

5.   Expiration Date.  Effective February 1, 2002, Item 7 of the Basic Lease
     ---------------
Provisions shall be amended in its entirety to read as follows:

     a.   With respect to the Original Premises and the Expansion Premises,
          December 2, 2003 (as adjusted pursuant to Article 1, Supplemental
          Lease Provisions).

     b.   With respect to the Second Floor Premises, January 31, 2006 (as
          adjusted pursuant to Article 1, Supplemental Lease Provisions).

     c.   With respect to the Third Floor Right of First Refusal Premises, May
          31, 2003 (as adjusted pursuant to Article 1, Supplemental Lease
          Provisions).

6.   Amendment of Exhibit A.  Effective February 1, 2002, Exhibit A attached
     ----------------------                               ---------
hereto shall be added to and made a part of Exhibit A attached to the Lease.
                                            ---------

7.   Amendment of Rider 1.  Effective as of February 1, 2002, Paragraphs 1 and 2
     --------------------
of Rider 1 of the Lease shall be amended in their entireties as follows:
   -------

                                       3
<PAGE>

1.  If, and only if, on the Expiration Date applicable to the Original Premises
and Expansion Premises and the date Tenant notifies Landlord of its intention to
renew the term of this Lease (as provided below) with respect to the Original
Premises and the Expansion Premises, (i) Tenant is not in default under this
Lease, (ii) Tenant then occupies at least ninety percent (90%) of the Agreed
Rentable Area of the Original Premises and the Expansion Premises and the
Premises then consist of at least all the Original Premises and the Expansion
Premises and (iii) this Lease is in full force and effect, then Tenant, but not
any assignee or subtenant of Tenant, shall have and may exercise an option to
renew this Lease with respect to the Original Premises and the Expansion
Premises for two (2) additional terms of seven (7) years each (each, an
"Original Premises Renewal Term") upon the same terms and conditions contained
in this Lease with the exceptions that (x) this Lease shall not be further
available for renewal after the expiration of the second Original Premises
Renewal Term and (y) the rental for each Original Premises Renewal Term shall be
the "Renewal Rental Rate", but in no event will the Base Annual Rent be less
than the Base Annual Rent applicable to the Original Premises and the Expansion
Premises for the last twelve (12) calendar months of the preceding term of the
Lease.

If, and only if, on the Expiration Date applicable to the Third Floor Right of
First Refusal Premises and the date Tenant notifies Landlord of its intention to
renew the term of this Lease (as provided below) with respect to the Third Floor
Right of First Refusal Premises (i) Tenant is not in default under this Lease,
(ii) Tenant then occupies the entire Third Floor Right of First Refusal
Premises, and (iii) this Lease is in full force and effect, then Tenant, but not
any assignee or subtenant of Tenant, shall have and may exercise an option to
renew this Lease with respect to the Third Floor Right of First Refusal Premises
for one (1) additional term of three (3) years (the "Third Floor Right of First
Refusal Premises Renewal Term") upon the same terms and conditions contained in
this Lease with the exceptions that (x) this Lease shall not be further
available for renewal and (y) the rental for the Third Floor First Right of
First Refusal Premises Renewal Term shall be the "Renewal Rental Rate", but in
no event will the Base Annual Rent be less than the Base Annual Rent applicable
to the Third Floor Right of First Refusal Premises or the last twelve (12)
calendar months of the preceding term of the Lease.

If, and only if, on the Expiration Date applicable to the Second Floor Premises
and the date Tenant notifies Landlord of its intention to renew the term of this
Lease (as provided below) with respect to the Second Floor Premises (i) Tenant
is not in default under this Lease, (ii) Tenant then occupies the entire Second
Floor Premises, and (iii) this Lease is in full force and effect, then Tenant,
but not any assignee or subtenant of Tenant, shall have and may exercise an
option to renew this Lease with respect to the Second Floor Premises for two (2)
additional terms of seven (7) years each (each, a "Second Floor Premises Renewal
Term") upon the same terms and conditions contained in this Lease with the
exceptions that (x) this Lease shall not be further available for renewal after
the second Second Floor Premises Renewal Term, and (y) the rental for the Second
Floor Premises Renewal Term shall be the "Renewal Rental Rate", but in no event
will the Base Annual Rent be less than the Base Annual Rent applicable to the
Second Floor Premises for the last twelve (12) calendar months of the preceding
term of the Lease. Each Original Premises Renewal Term, each Second Floor
Premises Renewal Term and the Third Floor Right of First Refusal Premises
Renewal Term are sometimes hereinafter referred to as a "Renewal Term".

The Renewal Rental Rate is hereby defined to mean the then prevailing rents
(including, without limitation, those similar to the Basic Annual Rent and
Additional Rent) payable by renewal tenants having a credit standing
substantially similar to that of Tenant, for properties of equivalent quality,
size, utility and location as the applicable portions of the Premises, including
any additions thereto,

                                       4
<PAGE>

     located within the area described below and leased for a renewal term
     approximately equal to the applicable Renewal Term. The Renewal Rental Rate
     will take into consideration the tenant inducements offered in the renewal
     transactions considered by Landlord in determining the Renewal Rental Rate.
     Notwithstanding the foregoing, with respect to the Original Premises ,the
     Expansion Premises and the Second Floor Premises, Tenant shall not be
     entitled to exercise the second renewal option unless Tenant exercises the
     first renewal option.

     2.  If Tenant desires to renew this Lease with respect to the Original
     Premises and the Expansion Premises, Tenant must notify Landlord in writing
     of its intention to renew on or before the date which is at least nine (9)
     months but no more than twelve (12) months prior to the Expiration Date
     applicable to the Original Premises and the Expansion Premises, or the
     expiration of the first Renewal Term, as the case may be.  If Tenant
     desires to renew this Lease with respect to the Third Floor Right of First
     Refusal Premises, Tenant must notify Landlord in writing of its intention
     to renew on or before the date which is at least nine (9) months but no
     more than twelve (12) months prior to the Expiration Date applicable to the
     Third Floor Right of First Refusal Premises.  If Tenant desires to renew
     this Lease with respect to the Second Floor Premises, Tenant must notify
     Landlord in writing of its intention to renew on or before the date which
     is at least nine (9) months but no more than twelve (12) months prior to
     the Expiration Date applicable to the Second Floor Premises, or the
     expiration of the first Renewal Term applicable to the Second Floor
     Premises, as the case may be.  Landlord shall, within the next sixty (60)
     days, notify Tenant in writing of Landlord's determination of the Renewal
     Rental Rate and Tenant shall, within the next twenty (20) days following
     receipt of Landlord's determination of the Renewal Rental Rate, notify
     Landlord in writing of Tenant's acceptance or rejection of Landlord's
     determination of the Renewal Rental Rate.  If Tenant timely notifies
     Landlord of Tenant's acceptance of Landlord's determination of the Renewal
     Rental Rate, this Lease shall be extended as provided herein and Landlord
     and Tenant shall enter into an amendment to this Lease to reflect the
     extension of the term and changes in Rent in accordance with this Rider.
     If (i) Tenant timely notifies Landlord in writing of Tenant's rejection of
     Landlord's determination of the Renewal Rental Rate and does not invoke its
     rights under Paragraph D below, or (ii) Tenant does not notify Landlord in
     writing of Tenant's acceptance or rejection of Landlord's determination of
     the Renewal Rental Rate within such twenty (20) day period, this Lease
     shall end on the applicable Expiration Date and Landlord shall have no
     further obligations or liability hereunder with respect to the Original
     Premises and Expansion Premises, the Second Floor Premises or the Third
     Floor Right of Right Refusal Premises, as the case may be.  If Tenant
     timely notifies Landlord in writing of Tenant's rejection of Landlord's
     determination of the Renewal Rental Rate and does invoke its rights under
     Paragraph D below (such notice, "Tenant's Notification"), this Lease shall
     be extended as provided herein and Landlord and Tenant shall enter into an
     amendment to this Lease to reflect the extension of the term and changes in
     Rent, with the Renewal Rental Rate determined in accordance with Paragraph
     D below.

8.   Security Deposit.  On or before February 1, 2002, Tenant shall pay to
     ----------------
Landlord the sum of $113,188.46, representing the Security Deposit for the
Second Floor Premises.

9.   No Representations.  EXCEPT AS PROVIDED IN THE LEASE, LANDLORD HAS NOT MADE
     ------------------
AND DOES NOT HEREBY MAKE AND HEREBY SPECIFICALLY DISCLAIMS ANY REPRESENTATIONS
OR WARRANTIES OF ANY KIND OR CHARACTER WHATSOEVER, EXPRESS OR IMPLIED, WITH
RESPECT TO THE SECOND FLOOR PREMISES, ITS CONDITION (INCLUDING WITHOUT
LIMITATION ANY REPRESENTATION OR WARRANTY REGARDING QUALITY OF CONSTRUCTION,
STATE OF REPAIR, WORKMANSHIP, MERCHANTABILITY, SUITABILITY OR FITNESS FOR ANY
PARTICULAR PURPOSE).

                                       5
<PAGE>

10.  Acceptance of the Second Floor Premises.  Tenant hereby accepts the Second
     ---------------------------------------
Floor Premises for all purposes.

11.  No Brokers.  Tenant warrants that it has had no dealings with any real
     ----------
estate broker or agent in connection with the negotiation of this Amendment,
excepting only Ford Alexander with Colliers Oxford Commercial and Cushman &
Wakefield, Inc. and that it knows of no other real estate brokers or agents who
are or might be entitled to a commission in connection with this Amendment or
otherwise in connection with the Lease.  Tenant agrees to indemnify and hold
harmless Landlord from and against any liability or claim arising in respect to
brokers or agents in connection with this Amendment other than Ford Alexander
with Colliers Oxford Commercial, it being agreed that Landlord shall pay only
Colliers Oxford Commercial a commission in connection with this Amendment
pursuant to a separate written agreement with such company.

12.  Authority.  Tenant and each person signing this Amendment on behalf of
     ---------
Tenant represents to Landlord as follows: (i) Tenant is a duly incorporated and
validly existing under the laws of the State of Delaware, (ii) Tenant has and is
qualified to do business in Texas, (iii) Tenant has the full right and authority
to enter into this Amendment, and (iv) each person signing on behalf of Tenant
was and continues to be authorized to do so.

13.  Defined Terms.  All terms not otherwise defined herein shall have the same
     -------------
meaning as assigned to them in the Lease.  Except as amended hereby, the Lease
shall remain in full force and effect in accordance with its terms and is hereby
ratified.  In the event of a conflict between the Lease and this Amendment, this
Amendment shall control.

14.  Exhibits.  Each Exhibit attached hereto is made a part hereof for all
     --------
purposes.

15.  Entire Agreement.  This Amendment, together with the Lease, contains all of
     ----------------
the agreements of the parties hereto with respect to any matter covered or
mentioned in this Amendment or the Lease, and no prior agreement, understanding
or representation pertaining to any such matter shall be effective for any
purpose.

                            Execution Page To Follow

                                       6
<PAGE>

     IN WITNESS WHEREOF, the parties have executed this Amendment as of the date
first above written.

                              LANDLORD:

                              THE PRUDENTIAL INSURANCE COMPANY OF AMERICA, a New
                              Jersey corporation

                              By:   Hill Partners Management Company, Inc., its
                                    authorized agent



                                    By: /s/ Beth Ann Signor
                                        -----------------------------------
                                    Name:   Beth Ann Signor
                                    Title:  President


                              TENANT:

                              VIGNETTE CORPORATION, Delaware corporation



                              By: /s/ John J. Ciulla
                                  -----------------------------------------
                              Name:   John J. Ciulla
                              Title:  Chief Information Officer

                                       7
<PAGE>

                                   EXHIBIT A

                      FLOOR PLAN OF SECOND FLOOR PREMISES

                                       1