<PAGE>

                                                                   EXHIBIT 10.36

                           Form of Investment Letter


                      [LETTERHEAD OF ZEFER APPEARS HERE]



                               September 10, 1999


[name]
[address]



     Re:  Investment in ZEFER Common and Senior Preferred Stock

Dear [name]:

     As we have discussed, you have been invited to invest in ZEFER's common and
senior preferred stock. Your participation will require that you make a capital
commitment of up to $[________] for the benefit of ZEFER Corp., as further
described below. A copy of the Company's Certificate of Incorporation, as
amended, which describes the relative rights of the common and senior preferred
stock, is attached as Exhibit A.

     By agreeing to the foregoing capital commitment, you will be entitled to
purchase [____] shares of ZEFER common stock at a price of $[___] per share and
will be required to purchase up to [___] shares of ZEFER's senior preferred
stock at a price of $1,000.00 per share from time to time as the Company
receives funding in respect of its capital commitments from GTCR Golder Rauner
LLC ("GTCR"). For example, to date GTCR has purchased approximately 19%, or
$18,000,000, of senior preferred stock in respect of their total capital
commitment for senior preferred stock of $94,200,000. By making this capital
commitment, you will be required to fund 19% of your commitment and to make
additional purchases on a pro rata basis with GTCR as additional funds are
needed by the Company. You will be provided notice of future fundings and
arrangements for the sale to you of additional shares of senior preferred stock
will be made at that time. Your commitment will expire upon the earlier to occur
of an initial public offering of the Company's common stock or upon fulfillment
of the capital commitment.

     In order to purchase the shares of common stock and to purchase the number
of shares of senior preferred stock required to be purchased by you as of the
date hereof, please sign the enclosed copy of this letter and send the signed
letter together with a check in the amount of $[_______] to Deirdre Aubuchon,
Vice President, Finance, ZEFER Corp., 711 Atlantic Avenue, 4/th/ Floor, Boston,
MA 0211 in the return envelope provided for your convenience.
<PAGE>

[name]                                                      September 10, 1999
Page 2

     Of this amount, $[_______] will be used for the purchase of ZEFER common
stock and $[____] will be used for the purchase of [__] shares of ZEFER senior
preferred stock. After giving effect to the foregoing issuances of common and
senior preferred stock, the balance of your commitment will accordingly be [___]
shares of ZEFER senior preferred stock.

     By signing in the space provided below, you agree to the foregoing capital
commitment and acknowledge that the issuance of the shares of common and senior
preferred stock by the Company hereunder is expressly made in reliance on such
commitment. Further, you agree that the investment representations made on
Exhibit B hereto are true and correct in all respects. In addition, attached as
Exhibit C is a copy of the Company's Stockholders Agreement (the "Stockholders
Agreement"). By signing in the space provided below you also agree to become a
party to the Stockholders Agreement, if you are not already a party.

     Please call if you have any questions regarding the foregoing and thank you
for your continued support of ZEFER.

      Regards.


                                             Sincerely,



                                             Sean W. Mullaney
                                             Executive Vice President and
                                                  General Counsel

SWM/jc
Exhibits


ACCEPTED AND AGREED TO:


----------------------------------
Name:


               This Form of Investment Letter was issued to and accepted by the
      executives of the Registrant (or the affiliates thereof) listed below. The
      only material differences among the respective Investment Letters are the
      following:


        (i)    the aggregate dollar amount of capital commitment,
        (ii)   the number of shares of common stock and preferred stock to be
               purchased,
        (iii)  the per share purchase price for the common stock,
        (iv)   the amount of the initial investment,
        (v)    the amount of the initial investment to be applied to the
               purchase of common stock,
        (vi)   the amount of the initial investment to be applied to the
               purchase of preferred stock, and
        (vii)  the number of shares of preferred stock to be initially
               purchased.

      The table below sets forth the above information with respect to each such
      executive.

<TABLE>
<CAPTION>
                                  Total      Total       Common                    Initial      Initial     Initial
                    Aggregate     Common   Preferred    Purchase     Initial       common      Preferred   Preferred
Executive           Investment    Shares     Shares       Price     Investment     Purchase     Purchase    Shares
---------           ----------    ------     ------       -----     ----------     --------     --------    ------
<S>                 <C>           <C>      <C>          <C>         <C>            <C>         <C>         <C>
Carol Boudreau        $350,978    71,868        339       $0.17        $74,978      $11,978      $63,000        63

Gerry Dube            $314,443    61,692        291       $0.38        $77,443      $23,443      $54,000        54

Mullaney
Investment, LLC       $200,855    41,128        194       $0.17        $42,855      $ 6,855      $36,000        36

James Slamp           $104,814    20,564         97       $0.38        $25,814      $ 7,814      $18,000        18

Martha Stephens       $100,427    20,564         97       $0.17        $21,427      $ 3,427      $18,000        18

Frank Torbey          $100,427    20,564         97       $0.17        $21,427      $ 3,427      $18,000        18

Thomas Waite          $145,876    28,620        135       $0.38        $35,876      $10,876      $25,000        25

David Lubin           $174,971    35,828        169       $0.17        $36,971      $ 5,971      $31,000        31

Richard Nolan         $100,427    20,564        97        $0.17        $21,427      $ 3,427      $18,000        18
</TABLE>

<PAGE>

Exhibit B


                          INVESTMENT REPRESENTATIONS


     1.  Unregistered Stock. The Undersigned is fully aware that the ZEFER
Common and Senior Preferred Stock ("Company Stock") he or she shall receive is
being issued and sold under an exemption from registration under the Securities
Act of 1933, as amended (the "Act"), that he or she is acquiring the Company
Stock without being offered or furnished any offering literature or prospectus,
that this transaction has not been approved or reviewed by the United States
Securities and Exchange Commission or by any administrative agency charged with
the administration of the securities law of any state and that financial
statements and other documents pertaining to the Buyer have been made available
to the Undersigned and the Undersigned's representatives, including the
Undersigned's attorney and accountant.

     2.  No Duty to Register. Except as may otherwise be provided in any
registration rights agreement between the Undersigned and the Company, the
Undersigned realizes that, in the absence of the availability of Rule 144 under
the Act, any disposition by him or her of the Company Stock may require
compliance with an exemption under the Act or a registration under the Act, and
that the Buyer is under no obligation to take any action to make any such
registration or exemption so available.

     3.  Investment. The Undersigned is acquiring the Company Stock for
investment for the Undersigned's own account and not with a view to, or for
resale in connection with, any unregistered distribution thereof, and the
Undersigned has no present intention to sell, convey, dispose of or otherwise
distribute any interest in or risk related to the Company Stock except pursuant
to an effective registration statement or in a manner consistent with the
requirements of the Act and the specific exemption from the registration
requirements of the Act relied upon by Buyer. The Undersigned understands that
the Company Stock the Undersigned shall receive has not been registered under
the Act by reason of a specific exemption from the registration provisions of
the Act which depends upon, among other things, the bona fide nature of the
investment intent as expressed herein.

     4.  Ability to Bear Risk. The Undersigned confirms that the Undersigned is
able (i) to bear the economic risk of this investment, (ii) to hold the Company
Stock for a substantial period of time, and (iii) presently to afford a complete
loss of the Undersigned's investment.

     5.  Other Agreements. The Undersigned acknowledges that the transfer of the
Company Stock that the Undersigned is receiving pursuant to this Agreement is
also subject to the restrictions contained in the Stockholders Agreement