To my knowledge, Exchange 2007 is x64 only, Server 2008 and Windows 7 were supposed to be 64 only, but Microsoft chickened out and made 32 bit versions.

If they had stuck to their plan of making all the server editions/business software x64 only, the transition would have been a much smoother process.

They just have to grow some balls and refuse to release new x86 systems, which will force software companies to pull their head out of their anus and create x64 software.