If you're buying the OS new, then I'd consider getting Vista 64 for now since it comes with a free Windows 7 upgrade (which is hopefully better than XP).

If you can wait a few weeks, then you should compare the price between what you're paying and what you could get at www.buyxg.com. I have a very similar system to yours for $1,654 including assembly, shipping, and extras that you don't have listed (such as hard drives including a small SSD, wireless keyboard & mouse, etc).