Until recently, I was having problems with fullscreen video in Windows on my new T61 Thinkpad, which uses an NVidia Quadro NVS 140M display adapter. Video would regularly flicker when fullscreen was enabled in a variety of players, including Windows Media Player and various embedded Flash players, and had to be taken out of fullscreen and put back - sometimes as many as 10 times - before the image was stable.
After doing a bit of hunting around yesterday, and noticing that at least one other person had the same problem, I came to the conclusion that it was power-saving based - my suspicion is that the refresh rate is reduced under some power-saving circumstances.
The following set of steps seems to remove the problem (or, to be more exact, I haven’t seen the problem return since following them):
Open the NVIDIA control panel (from the Start Menu or the system tray).
Navigate to Mobile / Change PowerMizer settings.
Select Not manage my power consumption (Disable PowerMizer).
Hope this helps someone else.