One good catch-all thing to try is make sure you have the latest drivers for your graphics and sound cards.
Also, make sure that Direct X is up to date on your system (although if you have XP Service Pack 2, it should be).
http://www.microsoft.com/directx
Also, your Media Player may not be using the best settings. Which Media Player are you using? If it is WMP10, click the down arrow in the title bard, then "Tools", the "Options", the "Performance". If you can, drag the "Video Acceleration" slider to Full.
Click "Advanced", then "Use Video Mixing Render" and "Use overlays" for both Video Acceleration and DVD video.