Originally Posted by MacLeod
If you can afford a GTX580, you should definitely get it. It will give you playable framerates in any game at 1920x1200.
You're gonna want to upgrade that CPU as well. Grab you a Phenom II X4 to go with the 580 and you'll be set.
On the back of my Fallout New Vegas box, it does say that the game is enhanced for Multi-core, so the CPU could be the problem, as that GTX 285 is a very good last generation top end card. And cramming a GTX 580 into that rig is going to be a waste, as you wont get the most out of it while the CPU still holds you back.
You could build a new rig, and simply put in your GTX 285 and it will still be great for games for quite a while. AMD's 6970 comes out soon too. So while you build/sort out the rig and hold off on the GPU upgrade, there could be a price war with the top cards if AMD pull something out the hat, and you might save some money, or heck, switch to AMD
EDIT: may wanna build it before VAT goes upto 20% next year.