If you install windows on a 64 bit processor it will work JUST like a 32 bit processor, you won't notice any difference... and windows 64 is overhyped, you don't get any performance increase... Here is a decent article describing what windows 64 is all about ->
http://www.tomshardware.com/2005/08/23/windows_xp_x64/
"Some programs run slightly faster, others slightly slower. At the end of the day, the difference is not noticeable."