Yep. I just upgraded myself a few weeks ago to a quad core intel 6600.

Also keep in mind you'll want to toss in a bigger power supply, and a real video card. a psu and video card will run you an additional $250 or so. (My psu was $70, and the video card I have in my system if from my old one, but can be had for about $170 shipped.)

If that puts you over budget, consider the gateway quad core 6600 system best buy has as well.. that's the system I purchased.

http://www.bestbuy.com/site/olspage.jsp?skuId=9032316&type=product&id=1218010533213

Memory is pretty cheap now, and you can kick the system up to the max 8 gb for about $35 more.

Way too many people take way too many things way too seriously.