If you're going to put that kind of money into a desktop, I would seriously consider building it yourself, and everyone here will probably be echoing my sentiments. It's cheaper to buy the parts individually, plus you don't have to stick to what companies offer, you can generally get newer bits of kit, like ATI's new 5970, which is the best graphics card you can buy.

If you don't know how or are worried about doing it, you can always speak to some tech savvy friends to help you build it, there are also plenty of sites that will tell you how to do it.