How can I clear my computer hard drive without and OS disk?

I just sold my computer on eBay and I need to clear out my hard drive for obvious reasons. Is there any way I can do this without my OS disk? I don't have it any more and I need to clear it. Thanks...How can I clear my computer hard drive without and OS disk?
I recommend Darik's Boot and Nuke.Darik's Boot and Nuke (';DBAN';) is a self-contained boot disk that securely wipes the hard disks of most computers. DBAN will automatically and completely delete the contents of any hard disk that it can detect, which makes it an appropriate utility for bulk or emergency data destruction.





Please note: If the CIA or FBI is after you, destroy the hard drive. It is possible to recover data even if it has been erased and written over many times.How can I clear my computer hard drive without and OS disk?
download and burn one of these to a disk -


http://www.dban.org/download


http://www.killdisk.com/


***or install Linux so they can see it works in pictures...don't worry about setting it up just install linux...
sledge hammer, lighter, and hairspray! :) you can't with out an OS. good luck
yes it is simple, go to windows explorer, win+e, right click on each driver one after the other left click on format .