So I take you actually have never used x64?
My recommendation is to definitely get x64 if you have the capability. It's built off of Windows Server 2003, and is a lot more solid overall. I have been using it since it came out. Oh and yes, I suppose now you will have to actually READ what you are about install to ensure it works on 64-bit systems (although most of the time it isn't a problem anyways). Or, as tominated mentioned, wait for Vista x64.