My suggestion to you is either save money to buy a new computer, even if you got a better graphics card, runn with 3gigs of Ram, and a cpu that is minimum specs. It wouldn't be worth it... You will get lag, your FPS will be low. Not trying to break your spirits here about your computer, but if you want decent game play with very little lag and decent performace of play, especially if your going to raid or pvp, Id upgrade.
Just a sugestions