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. :)