Windows Server 2003: 64 bit or 32 bit ?

The server can do either.

The question is; which one can do all that you need to do?

64 bit can address much more memory and some applications won't run in 32 bit Windows (e.g. Exchange 2007), but other software may not be compatible with x64 Windows (e.g. some older Antivirus versions and I believe Exchange 2000 doesn't like x64 either).

I'd check if everything you want to run can run on x64, and if so, get that. It is where the world is moving to (slowly, but surely).

Thank you very much. That was exactly the kind of answer I was looking for.