Are you using a USB wireless adapter? I know it sounds crazy, but my brothers game would stutter like CRAZY when he used one, on set intervals.. like every 1 second it would stutter for .5 seconds. (not lag, but the actual video would stutter).
We tried everything, till one day i borrowed his internet adapter and my computer started doing the same thing. Noone has been able to explain to us why a USB internet card would cause video problems.
