What you will need to do is this, if you can.
1. Install the drive as a second drive on a computer and see if you can read the data from it.
2. If you can read the data from it. There is an iso disk image called dban boot and nuke that you can use. It does work on the same principal as DOD eraser programs. This is a free program but it will cost you a cdr disk. You can "Write" the iso with IMG burner (also a free program).
If you do not want to boot and nuke iso, then you can format the hdd or delete all of the information from the hdd and goto
www.piriform.com , there is a prog called recuva. Download and install the prog, it's free. Search the drive and when the files come up in the wizard, check all, right click, select delete all checked and the files will be gone forever.
After that, you might want to remove the drive and see of you can take it apart. Most hdd disk media is a type of metallic disk. This disk will be hard in density and very shiny. You should be able to "multilate" the disk and permantly destroy it, keeping your information safe.