You are only able to use the 64bit edition of Exchange 2007 in production, but you are allowed to download and use the 32-bit edition of Exchange 2007 for any of the following three purposes: testing, training, or administrative purposes. You can even use the 32-bit edition of Exchange, which is only available as a standard edition, to test CCR. After 120 days the 32-bit evaluation version will expire. It is possible to use this 32-bit edition of Exchange to deploy the Exchange administrative tools on any of your 32-bit OS administrative workstations, or to prep your forest on your Schema Master itself when it is running on a 32-bit OS.