Erasing an Hard Drive with Bad Sectors

I believe I posted this earlier to the wrong forum, so I'll repost it appropriately here.

Dell has determined that my NTSB hard drive on my Studio 1555 is faulty, so they have sent me a new hard drive and want the old one sent back to them. I don't intend to send them my old drive without first cleaning the disk of personal information, but when I used Darik's Boot and Nuke, the program reported bad sectors on the hard drive and aborted the HD wipe after only four seconds into the process, so at least that particular software application won't do the job. Dell won't allow me to physically damage the HD before sending it back, so is there another way I can render it unreadable without doing damage?

I have heard that a magnet will wipe it, but I don't know how that works. The strongest magnet I have is probably a ten or fifteen pound one from an audio speaker.

Any help you can give? For both work and college purposes, I'm on an extremely tight deadline to get the new hard drive in and get up and running again, unfortunately.

Thanks.

i have also hear that magnets are not good for the hard drives but i don't rly know for sure. something you can do is put in the hard drive and just put in the and reformat with the windows cd. if u really wanna mess up the data let it start installing then power down.
if you cant install windows then the hard drive is broken to the point that it would not be ez to get data off it, they would have to open it up in a clean room and the person would rly have to know what they are doing.