Forget dual core.. quad core is the minimum you want now, Tiny. You can get a good quad core system with a new video card, 8 gb of memory, and 750 gb hd space for about $900 total.

(I just upgraded myself to this configuration.)

PM or email me for details

Videocard wise, I use tom's hardware guide, because they have price tiers, with the best card chocies by price. Under $200, they list a ati card, and over $200, they list both a ati card and a nvidia card. I've got the under $200 card, and it rocks seriously, and I haven't seen any opengl issues with it at all.

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