Overwrite data to sell computer

I've got an older Dell that is running Win XP and I'd like to see if anyone knows of any programs that will allow me to overwrite just select portions of the hard drive so I don't have to re-install XP and all the programs?

Pop in your Dell disc and format the hard drive.

Do what harryb2448 says ...or...Take the drive out and hammer a nail throw it. When I buy PC computers at the thrift store I prefer the HD is gone as it sells for $6.00.

I'm not destroying the drives. There are two, 2 year old expensive ultra quiet Samsung's. I replaced them and they need to be sold with the computer. I want to computer to be working and all the software fully functional. I need to write over the previously deleted files/free space.

Here's the LINK to the free "Eraser" program for Windows. It's actually donation ware but it reportedly works well. Follow directions carefully so as not to overwrite or erase the OS.

Regards.