There have been lots of questions about the Microsoft Windows 32 bit versus 64 bit situation. Many people out there are wondering which version they should get and what the differences between the versions are.
The answer to the question is really easy. If you are having to ask, you are better off with the 64 bit version for now. Only the computer savvy will easily deal with the lack of support for these operating systems right now.
Do you need a 64 bit os? Absolutely not at this time. The biggest advantages that these systems give is the ability to use more memory. Since most computers are fine with 2 gb and will be good with up to 4 gb for the next couple years there is no reason to go with the 64 bit operating systems.
There will be a messy transition from 32 bit systems to 64 bit systems in a couple years. My suggestion is to stick with the well supported Microsoft 32 bit system and then move to the 64 bit systems when two things happen.
First, they are fully supported. You will find a lot of current hardware lacking the 64 bit drivers. Second, until programs or games require more than 2 gb of ram. It does you little good if you have 4 gb of ram, but your computer is only using 2 gb of it. This is the case for the majority of computer users at the moment.
BTW, the answer is the same whether you use XP or Vista, it makes little difference. In fact, you should be less likely to use the higher bit os with XP because it is even less supported.