Many people have their ATI drivers crash when they try to watch movies, or even youtube when simultaneously mining under windows. There is an easy fix.
1) disable windows aero. Not even sure if thats needed, but its a good idea nonetheless
2) disable hardware acceleration in flash. Just right click a flash movie (youtube clip), chose settings, uncheck "hardware acceleration". If you have a somewhat decent CPU, you wont notice any difference, except, it will no longer crash.
3) to watch dvd, h264 etc movies, use an alternative mediaplayer. I use smplayer:http://smplayer.sourceforge.net/downloads.php
Start smplayer, go to options, preferences, general, video, output driver and set it from Direct3D to DirectX fast. Optionally, go to Performance, and set decoding threads to 2. That helps prevent stuttering for me.
Thats it. Havent had a driver crash since I made those settings, while cgminer is constantly running in the background
BTW, I suspect you can change this in VLC too if you prefer VLC. I havent tested this as thoroughly, but if you go to extra, preferences, video, output, you have the option DirectX (directdraw) which does the same I suspect. If that doesnt help, try disabling the hardware acceleration /overlay option.
Feedback on VLC settings that work are welcome.