I have an nVidia 8600GT card (made by EVGA) on a machine with Windows Vista (AMD Athlon X2 processors) and four gigs of ram. It runs pretty good, but I have had some slow/choppy/stuterring video playback issues whenever watching flash videos on Youtube or other sites. The problem is there with both Firefox and IE flash videos, but is maybe worse with Firefox. I also tried Linux with nVidia's binary drivers and it was about the same. I downloaded EVGA precision which allows me to control stuff like the fan and clock speed. The card's temp (in both Vista and Linux) is usually at 66C when idle (not playing a game or watching anything). It goes up a little when watching a video (maybe 68-72C).

Any ideas on how to fix this?

UPDATE: The issues are both with full screen and embedded flash videos. I have Flash 10.0.32.18 (always make sure I use most recent for security), and the CPU is an AMD Athlon 64 X2 Dual Core Processor 4000+ at 2.11 GHZ. The current GPU driver installed is the most recent GeForce one from last July.