Regarding Video cards and VRam size. A lot of what 335th_GRAthos said is corrent, but it also depends on the number of monitors you're playing on and the resolution. If you're on a typical 20" monitor, playing at 1600x900 or somewhere around that area, you're probably going to be fine with a 2GB card for all the eye candy. Going to higher resolution with everything maxed is when you start getting into the 2.4GB VRAM requirement he mentioned.

When going for the 2GB+ cards, be mindful if they are single or dual GPU cards. A dual GPU card is pretty much an SLI/XFire setup that's confined to one card, so don't expect amazing gains.

Believe it or not, the biggest limiting factor isn't hardware, but software. The game was released in what could be called a "broken state" so it's requiring more system resources and horsepower than it really should need. If you can, wait for the new Graphics engine to be released and see what happens after that. Maybe it will be the 20-50% FPS increase that Luthier was saying, but it might also be another flop. Remember those guys who bought cutting edge systems for $2000 during the summer of 2010? Well they're getting their systems spanked by people with $800 PC's now, and they're lucky to have their games playing at anything higher than medium across the board.

HOLD ON TO YOUR MONEY! You're waited damn near a year for this game to be playable, just wait another month or two! The best thing that can happen is component prices drop, you save money, and getting a better system than if you bought now.