I have developed this problem myself, so have searched for a solution. And I thought I found one.
However, I had been using my OCZ Modxstream-Pro 700w when this hinky video/audio problem started, so I am hoping my ps is not the problem. It has 25amp 12v rails.
I actually started noticing the problem shortly after the latest patch for Win XP sp3 was installed.
I only have problems with games, even those that I have played through w/o any such problems (Dragons Age), COD4, Mass Effect........
Just FYI, I am running an Asus P5QL-EPU mb, Intel Q9550, Seagate ST3250310AS hd, (2)Corsair DDR2 800 sticks, and using the onboard VIA HD audio