you can still go back to the old drivers. go to the control panel, >> click system >> click the hardware tab >> click the 'device manager' tab >> double click your video card >> click the driver tab >> and click the 'roll back' button. and reboot.
EDIT: what version of detonators are you using now???
You can usually find older versions of drivers around. If you've still got the driver CD that came with your card you could try those, else look on Nvidias site to see if the keep an archive of older versions of detonators.
Failing all that you could probably do with upgrading your computer if you've had it for 2 1/2 years
thats my thought too, a majority of the movies I find on Kazaa are DIVX avi's. A great many will not play correctly on windows media player. Get the divx codec bundle, and try opening the movie in the divx Player instead.