Just wanted to post a solution I had to a problem I have been having lately since I installed my ATI All-In-Wonder X800 (AGP).

Whenever I would open an application requiring 3d rendering (quake 3, Wolfenstein, etc) the game would crash about a minute in and give me a sig 11 code.

I took apart my computer to realize I was running a 300 Watt power supply. I replaced it with a 500 watt and everything runs fine now (and the system is faster).

So if your getting random crashes (sig 11) from graphics intensive tasks. Check your PSU.