EDIT: FORGET ORIGINAL POST
You said you're willing to spend $300. Here you go. Sell your current machine for $150, and buy this for $273
. I tried to find something that would total it to exactly $300, but couldn't. Adding another 2GB stick would make it $309. Plus, shipping and handling would probably make it $290 or so.
AMD X2 5000+, brand-spankin' new HD4850 (eats the 8800GT and the 9800GTX both for breakfast)
, 2GB DDR2-800 (i screwed the memory thing up again, it should be the same price, my bad), 400-watt power supply and sleek mid-tower from Rosewill.