It was an old 233MHz machine that I had turned on looking to see if there was anything that needed saving off the hard drive. It had just finished its POST when I heard snaps, crackles, and pops and then saw fire. I turned off the power strip that the computer was plugged into and rushed into my computer lab for the CO2 fire extinguisher. Alas, by the time I returned, the fire was out. I sprayed it anyhoo. (Actually, I sprayed the one next to it first, accidentally.)
So now I've had a real computer fire - pretty cool. (Well, cool in that it wasn't *my* computer and there wasn't a lot of collateral damage, especially to *me*.)
The hard drive, BTW, didn't have anything useful on it after all. I ended up reformatting it and using it in one of the first grade rooms.