Four quick and dirty methods, depending on your paranoia level, how many tools and how much time you have. Its a simple case of determining acceptable loss versus the economy and efficacy of destruction (in other words, unless you have something the FBI or NSA wants, go for the easier solutions):

1. Trivial: Destroy the IDE connector. If you're just hiding your porn, few people will bother to rebuild an IDE connector.
2. Simple: Push a small screwdriver through the plastic filter port on the side of the drive, and scratch it over the surfaces of the platter. Scratched drives can't be read.
3. Easy: Undo the 7 or so Torx screws holding the cover, expose the platters, and give them a good hard *whack* with the ball end of a ball-peen hammer. Dented drives can't be read, either.
4. Easy, time consuming: Disassemble the drives, and rub each platter over some nice diamond sandpaper.

-Dan

Read Foiling the Cracker; A Survey of, and Improvements to Unix Password Security - I published it nearly 20 years ago, and people are still arguing over password security? My personal password is 15 characters long. My root password is 20 characters long. Both are trivial for me to remember, and effectively impossible to crack (they're passphrases containing upper ad lower case, numbers, punctuation and obfuscation of multiple words not found in any permutation dictionary. Users on my system are REQUIRED to have strong passwords of their own devising (so that they can remember them). What's so hard for people to understand about that? You can't have good security and be lazy.