|I recently had to make this decision myself. In the end, I went with Vista x64 as I wanted to use 8GB of RAM.|
There are quite a few benefits to the 64bit version of Windows. I have had no compatibility issues with software (all of my 32 bit software works just fine) and I can also run new 64bit software. The one problem is with drivers. Before going to 64bit, make sure all of the hardware critical to you (including sound cards, printers, USB devices, EVERYTHING) has a 64bit driver available. Many devices (like my D-Link skype adapter) do not have 64 bit drivers and therefor won't work.
If you do go 64-bit, I would strongly suggest Vista over XP. While people complain about Vista, when it comes to the 64-bit versions, Vista is much better than 64-bit XP.
Finally, if you stick with 32-bit, you should still get a 64-bit processor. Your 32-bit OS will still install fine, but you'll have the ability to upgrade later on.
Free Computer Tips and more:http://RyanTAdams.com
Paid Tech Support: Black Diamond