Hi again,
I don't understand every bit of what you are saying, but here is for my part what I know about my machine.
iMac 27", running full screen mode at max resolution (2560 * 1600), 4Gb Ram 1067 Mhz, Intel Core 2 Duo 3,06 GHz. OS X is up to date with the latest version, 10.6.4. For more information on my system, I copied all the information from the sys info tool. You can find it below on RTF format (if you have easier with XML, feel free to ask).
My system is also very clean, as I formatted about a week ago, and don't have anything fancy installed. I have steam installed, and Bootcamp not installed at all.
Hope this help,
PS : Now that I think about it, could it be something to do with permissions in files ? There is no perms in windows, but they exist on Mac OS X. As someone mentionned about the song (i can't remember if it was a song playing when it crashed, but I do remember there was no music when I shut down, and it didn't hurted me hearing a music stopping... So it's a possibility that it crashed by the end of a song...)