Document:

<PAGE>

                                                                     Exhibit 4.2

                                   AMENDMENT
                           TO STOCKHOLDERS AGREEMENT
                          Dated as of October 2, 2000

     DDi Corp., a Delaware corporation (the "Company"), Bain Capital Fund V,
L.P., Bain Capital Fund V-B, L.P., BCIP Associates, L.P., and BCIP Trust
Associates, L.P., and the Other Investors and Managers signatories hereto:

     1.   Reference to the Stockholders Agreement; Definitions.  Reference is
          made to the Stockholders Agreement dated as of April 14, 2000 (as
          amended, the "Stockholders Agreement"), among the Company and the
          holders of its equity interests (including without limitation the
          other parties hereto).  Terms defined in the Stockholders Agreement
          and not otherwise defined herein are used herein with the meanings so
          defined.

     2.   Amendment. Pursuant to Section 12.2 of the Stockholders Agreement,
          each Investor and each other signatory hereto hereby agrees to amend
          Section 8.4.4 of the Stockholders Agreement by deleting the second
          sentence thereof and replacing it with the following sentence:

          "In the case of any Public Offering that is not the IPO or effected
          pursuant to Section 8.2A, each holder of Shares agrees to enter into a
          reasonable form of agreement, approved by the Company, restricting the
          Transfer of any Common Stock during the period beginning seven days
          immediately preceding and ending on the 90th day following the
          effective date of the registration statement used in connection with
          such offering if the underwriters managing such Public Offering demand
          such an agreement."

     2.   Miscellaneous.  Except to the extent specifically amended hereby, the
          provisions of the Stockholders Agreement shall remain unmodified, and,
          subject to the conditions contained in this Amendment, the
          Stockholders Agreement is hereby confirmed as being in full force and
          effect.  This Amendment may be executed in any number of counterparts
          which together shall constitute one instrument, shall be governed by
          and construed in accordance with the laws of the State of Delaware,
          without regard to the conflict of laws rules of any jurisdictions.
<PAGE>

                                                                    Amendment to
                                                          Stockholders Agreement
                                                                 October 2, 2000

     In WITNESS WHEREOF, the parties have caused this Amendment to the
Stockholders Agreement to be executed and delivered as of the date first above
written.

                                         DDI CORP.

                                         By  /s/ JOSEPH P. GISCH
                                           --------------------------------
                                           Name:
                                           Title:

INVESTORS:
                                         BAIN CAPITAL FUND V, L.P.
                                         BAIN CAPITAL FUND V-B, L.P.

                                         By Bain Capital Partners V, L.P.,
                                                their general partner

                                         By Bain Capital Investors V, Inc.,
                                           its general partner

                                         By  /s/ EDWARD CONARD
                                           --------------------------------
                                           Name:
                                           Title:  Managing Director

                                         BCIP ASSOCIATES
                                         BCIP TRUST ASSOCIATES, L.P.

                                         By  /s/ EDWARD CONARD
                                           --------------------------------
                                           Name:
                                           Title: a general partner
<PAGE>

                                                                    Amendment to
                                                          Stockholders Agreement
                                                                 October 2, 2000

OTHER INVESTORS:
                                         CELERITY DYNAMO, L.L.C.

                                         By  /s/ [ILLEGIBLE]
                                           --------------------------------
                                            its Manager

                                         CELERITY LIQUIDS, L.L.C.

                                         By  /s/ [ILLEGIBLE]
                                           --------------------------------
                                            its Manager

                                         CELERITY DETAILS, L.L.C.

                                         By  /s/ [ILLEGIBLE]
                                           --------------------------------
                                            its Manager
<PAGE>

                                                                    Amendment to
                                                          Stockholders Agreement
                                                                 October 2, 2000

OTHER INVESTORS:
                                         CHASE MANHATTAN CAPITAL, L.P.

                                         By  /s/ [ILLEGIBLE]
                                           --------------------------------
                                            its

                                         CHASE SECURITIES INC.

                                         By  /s/ [ILLEGIBLE]
                                           --------------------------------
                                            its

                                         DI INVESTORS, L.L.C.

                                         By  /s/ [ILLEGIBLE]
                                           --------------------------------
                                            its
<PAGE>

                                                                    Amendment to
                                                          Stockholders Agreement
                                                                 October 2, 2000

MANAGERS:

                                         /s/ CHARLES D. DIMICK
                                         --------------------------------
                                         Charles D. Dimick

                                         /s/ BRUCE D. MCMASTER
                                         --------------------------------
                                         Bruce D. McMaster

                                         /s/ JOSEPH P. GISCH
                                         --------------------------------
                                         Joseph P. Gisch<PAGE>

                                                                   EXHIBIT 4.3

                                    AMENDMENT
                            TO STOCKHOLDERS AGREEMENT
                          Dated as of January 29, 2001

     DDi Corp., a Delaware corporation (the "Company"), Bain Capital Fund V,
L.P., Bain Capital Fund V-B, L.P., BCIP Associates, L.P., and BCIP Trust
Associates, L.P., and the other signatories hereto:

      1.    Reference to the Stockholders Agreement; Definitions. Reference is
            made to the Stockholders Agreement dated as of March 31, 2000 (as
            amended, the "Stockholders Agreement"), among the Company and the
            holders of its equity interests (including without limitation the
            other parties hereto). Terms defined in the Stockholders Agreement
            and not otherwise defined herein are used herein with the meanings
            so defined.

      2.    Amendment. Pursuant to Section 12.2 of the Stockholders Agreement,
            each Investor (constituting the Majority Investors) and each other
            signatory hereto hereby agrees to amend Section 8.3.1.1 of the
            Stockholders Agreement by deleting the phrase "20 days after the
            effectiveness" therein and replacing it with the phrase "8 days
            after the mailing by the Company by registered mail or overnight
            delivery".

      3.    Miscellaneous. Except to the extent specifically amended hereby, the
            provisions of the Stockholders Agreement shall remain unmodified,
            and, subject to the conditions contained in this Amendment, the
            Stockholders Agreement is hereby confirmed as being in full force
            and effect. This Amendment may be executed in any number of
            counterparts which together shall constitute one instrument, shall
            be governed by and construed in accordance with the laws of the
            State of Delaware, without regard to the conflict of laws rules of
            any jurisdictions.
<PAGE>

                                                                    Amendment to
                                                          Stockholders Agreement
                                                                January 29, 2001

      In WITNESS WHEREOF, the parties have caused this Amendment to the
Stockholders Agreement to be executed and delivered as of the date first above
written.

                            DDI CORP.

                            By  /s/ CHARLES D. DIMICK
                              --------------------------------
                              Name:
                              Title:

INVESTORS:
                            BAIN CAPITAL FUND V, L.P.
                            BAIN CAPITAL FUND V-B, L.P.

                            By Bain Capital Partners V, L.P.,
                                   their general partner

                               By Bain Capital Investors V, Inc.,
                                 its general partner

                               By  /s/ DOMINIC FERRANTE
                                 -----------------------------
                                 Name:
                                 Title:  Managing Director

                            BCIP ASSOCIATES
                            BCIP TRUST ASSOCIATES, L.P.

                            By  /s/ DOMINIC FERRANTE
                              --------------------------------
                              Name:
                              Title: a general partner

                                       2
<PAGE>

                                                                    Amendment to
                                                          Stockholders Agreement
                                                                January 29, 2001

OTHER INVESTORS:
                            CELERITY DYNAMO, L.L.C.

                            By  /s/ [ILLEGIBLE]
                              -------------------------------
                               its

                            CELERITY LIQUIDS, L.L.C.

                            By  /s/ [ILLEGIBLE]
                              -------------------------------
                               its

                            CELERITY DETAILS, L.L.C.

                            By  /s/ [ILLEGIBLE]
                              -------------------------------
                               its

                                       3
<PAGE>

                                                                    Amendment to
                                                          Stockholders Agreement
                                                                January 29, 2001

MANAGERS:

                         /s/  CHARLES D. DIMICK
                         ---------------------------------
                              Charles D. Dimick

                         /s/  BRUCE D. MCMASTER
                         ---------------------------------
                              Bruce D. McMaster

                         /s/  JOSEPH P. GISCH
                         ---------------------------------
                              Joseph P. Gisch

                                       4

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