a little late on this thread, but i'll put in some input ofr the next guy....
I hit a stripped screw scenario on my harddrive as well. I masking taped paper to the area around it to prevent metal shavings from getting into the works, and used my dremel w/ a cutoff wheel to carve a slot for a flathead- I don't remember if the screw was countersunk and stuck on the way out, or if it was a pan head type that wouldn't budge. at any rate, there was meat to cut into. Worked great, but was annoying. Actually, I think it worked great on one of them, the other I just cut the head entirely off, and removed with a needlenose once I got the drive out.
I thought the screws were stuck due to dissimilar metals between the magnesium chassis and the steel (or low-allow stainless) screw, with the aluminum hardrive possibly adding to the mix of cathodic current.
I replaced them with allen-head screws.
- - Dave