Thanks for the quick reply, anyways, I don't have any third party hardware. When it crashes this grey transparency drapes down over my screen and tells me to hold down the power button to restart.
Programs that I was running when the crashes occurred include: amsn, azureus, itunes,tagebuch, firefox, usually i have a finder window open, and really that's all. If I remember correctly it usually occurs when I have a fair amount of programs running at once...like the ones above.