Your CPU and RAM are good for the game.
Does the lagging happens even if you play at the lowest settings?
Try playing the game with no internet connection, no antivirus and no other programmes open. Does the lagging happens then?
Did you install the latest Nvidia drivers for your card?
m using internet,AVG 9 antivirus...
ya i have installed latest drivers for 8500GT.
obviously programs r close with its process from WTM(task mangr)....