If you don't have a quad-core CPU, I highly suggest getting one. You can get a decent quad-core for cheap nowadays, and you'll certainly see big performance boosts over dual or single cores.
As for video cards, I don't really know how to rate them, either. Pretty much, the more expensive it is, the better it is. ;p
As for video cards, I don't really know how to rate them, either. Pretty much, the more expensive it is, the better it is. ;p