I have just bought Black Ops for PC and i keep getting on and off lagg, my specs are over reccomended?

I know it is not my internet because i have tried on offline server with bots, and i think it maybe to do with my graphics card because the graphics in the game is also not great. I have put all the graphics down to minimum, could it possibly be my monitor? I am sure that my computer specs are over the recommended level. Thanks i really need some help.