OEM copy will be tied only to the computer you've installed it on - you can reinstall it whenever you like, but you can't install it on a different computer.
If you already own Windows Vista then get the upgrade version of Windows 7. You can still do a full, clean reinstall using your upgrade license so don't worry about that. In fact, moving between 32-bit and 64-bit systems usually requires a clean reinstall anyway.
Just make sure you've backed up everything you want to keep before you format your drive.
great thanks for the advice,i think i will do a clean install with a OEM windows 7 64 bit,its alot cheaper that way,thanks again