I have an 8800, which is supposed to be the minimum requirements to run the game...does anyone know how I can help to reduce lag?

I have an 8800, which I know is the bare minimum needed to run the game, but..I wasn't expecting this.

"Be advised-d-d-d-d-d-d, we have captured the contro-tro-tro-tro-trol point-t-t-t. I repeat-t-t, we have taken-aken-aken-aken the control point-oint-oint."

If I stumble onto the person and try to shoot them, then game over, im dead. The only way I can seem to get any kills is to just set up a bipod and wait for people to come to me, but still, even doing that everything is very laggy.

Does anyone know how I can maybe reduce the lag, at least a little bit? I read that at least a GTX560 is recommended but I dont have that kind of cash, so just buying a new video card is out of the question.

For the record, Campaign is fine, but it has lag spikes too.