Re: XP-32bit or Vista-64bit
You already have XP? If so, then it's not worth the extra cost to upgrade (because it would be an upgrade) to Vista.
If this were a new rig and you were choosing between the two, then Vista 64 would be the obvious choice.
AMD Phenom II X4 955 BE @ 4.0GHz + TU120E lapped - MSI 770-CD45 AM3 - 2x2GB OCZ DDR3 1333MHz - Sapphire HD 4870 - Samsung Spinpoint 500GB 7200RPM 16MB cache HDD - Tagan TG600-BZ Piperock - (Currently open test bed) - Windows Vista Home Premium 64bit.