Open it up and find the hard drive. Remove it (usually screws on either side hold it in place).

Now you're faced with a choice - these hard drive cases are darn near indestructible. A sledge hammer might do it in, but will take a few tries.
Merely breaking the circuit board on the bottom is not going to destroy the data - it can still be reconstructed by a professional (they take the discs out and put them into running drives). Soaking in acid for a few days is a possibility, but usually only serial murderers have vats of nitric in their garage.

The other option is to actually take the top off the hard drive, and find the disc inside. Looks a lot like a CD, but brownish. Scratch it up with sandpaper or break it, but this is where the bits live. You need to make sure they can never be re-assembled.

A really big magnet might work, but you have no way of knowing whether it did or not and how much. I recommend physically destroying the disc.

PS> One more weekend and I'm outa' here.

You've got plenty of options; bulk eraser, degausser, shotgun, sandblaster, dremel (or equivalent power drill) to make swiss cheese out of the platters, or same with a wire brush attachment, a mild acid on the platters (start with lemon juice to see if it will corrode, then work up to stronger stuff if required) or thermite.Have fun :)

Cool - I hadn't considered thermite. Thanks. I've got a few drives I need to wipe as well, and taking them apart is so laborious.

You can probably still get your data off the drive (and or erase it and use it as an external drive).

All you need is an external drive case, a screwdriver, a large whisky and a little patience. Actually you probably don't need the whisky. A beer would do. Or a cup of tea. Actually, not a cup of tea.

If you want to have more details, let me know. I do this every time I upgrade to a larger hard drive in my laptop....