Depending on how badly you want the data gone, you can download a program like Eraser 5.3, delete everything non OS, and write random data to the drive X times over. Then just format the OS off ... that should make everything go away with almost zero chance of recovery.
For real peace of mind, just go to office max and buy a 10 gig, 5400RPM drive for ~$50, swap 'em, and walk out with your old drive. Then either toss it in the trash or put it in your home machine and use it for whatever.