If you don't have a decent graphic card (or u are using integrated graphics) then you might lag when playing COD.

Before I install my current graphic card (ATI HD4670) I was using integrated graphics. When I was playing COD4 it was like.. lagging like hell... Even 800x600 will lag seriously...

But then now I am using my graphic card, even if i use highest resolution with maximum graphics quality everything is so smooth and nice. I can even play Devil May Cry 4 with max settings smoothly.

Juz my 2 cents