Whew!  You finally got Exchange 5.5 out of the picture and are now are focused on getting Exchange 2007 into your environment.  You have taken a good hard look at How to Prepare Active Directory and Domains and are sure that you are ready to prepare the AD for Exchange.  But...  You don't have a single Windows machine running x64.  You have read all of the warnings on running the 32-bit version Exchange 2007 in production.  You aren't looking to install Exchange, just prepare the schema.  Can you use the 32-bit version for that?

Yes, you can.  There are two instances in which you can use the 32-bit code in production and this is one of them.  Specifically, at Exchange Server 2007- Platforms, Editions, and Versions you will find:

"You can use the 32-bit version in production to extend your Active Directory directory service schema."

Interestingly, Scott Schnoll's mentions more about this on his blog: Exchange 2007: Platforms, Editions, Product Keys and Versions.  If you notice the similarities between the two articles with the similar titles, that might be because Scott is a Technical Writer for the Exchange team.  :)