If I read correctly, you're asking about 32 and 64bit and not the different types of vista - home, business, ulimate etc. I don't know much about computers but it has something to do with the computer architecture with the memory being 4 bytes wide for 32 bit and 8 bytes wide for 64 bit. Check out this wikipedia article for more info
64-bit - Wikipedia, the free encyclopedia (the article on 64-bit has more information than the 32-bit and compares them both) I'm pretty sure these numbers have to do with your processor. Hope that helps