said by JohnInSJ:
does your computer have more than 4gb of ram? If not, there is no reason at all to do it.
I agree with the conclusion, so I am hesitant to make this point, but there are advantages of the 64 bit version from a security standpoint. Supposedly the kernal is much better protected using the 64 bit version. Having said that I have seen so many 64 bit systems trashed by malware, rootkits, etc. that my feeling is in the real world there isn't that big a difference. The bad guys know how to get around the protection.