From microsoft site:-

Why does my video flicker?

A variety of issues may cause video to flicker in Windows Media Player. To troubleshoot possible causes, do the following:
•Check for video-card driver updates from the maker of your video card.
•Check for Microsoft DirectX updates by scanning for updates on the Windows Update Web site.
•Try a different acceleration setting for your video hardware:
1.
In Windows Media Player, click the Tools menu, and then click Options.
2.
On the Performance tab, in the Video acceleration area, drag the slider to None to use basic video-acceleration settings that work with most video hardware. For some video hardware, you must do the opposite (drag the slider to Full) to correct the problem.
•Microsoft NetMeeting Remote Desktop Sharing may cause video-performance problems with the Player. In this case, you will have to uninstall NetMeeting in order to improve Player performance. For more information, see NetMeeting Help.

Try updating your codecs:-

http://www.DivX.com

http://www.Xvid.org.

If none of these resolve the issue let me know