What system are you installing Windows on to?
You don't need to run the x64 versions in that case as you are unlikely to see any benefit. You could try the 32bit version of Vista or Windows Server 2008 which is quicker. Windows 7 or Server 2008 R2 is much quicker than Vista or XP in my experience but is still in beta phase so some things may not work as expected.
I tried Vista 32bit and 64bit and I found 64bit to run slow. I was just wondering has anyone tried XP? Is it faster? Because I think I may just have to install XP. (I have access to a lot of windows os)
Slow? Define slow. By all accounts, you're the first person I've ever heard to say they felt Vista32 was "faster" than Vista64.
XP is a joke. You have a beast machine, at least run a modern OS on it. Win7 64 is a good choice I'd say.