Open it up and take a look at the hard drive. If you can actually reach all the screws with your screwdriver, it's a snap. If one of the screws is surrounded by sharp mental spikes that are welded to the tower casing, well, not so much.

*glares at currently half unassembled computer on the floor and contemplates taking wire cutters to said sharp metal spikes*

Yeah, as you may have guessed, and doing this right now, because my mom needs files off of her 256MB worth of RAM Win ME computer and all of its disk drives are broken.