Then use the default not quick format during XP set up
To completely erase all data on the drive(s)
Click this to download Boot and Nuke
Click this for a guide to using Boot and Nuke
Use the autonuke option, which could take 8 hours or so to format a 200 GB Hard Drive, then when you run Windows set up, use the default, not quick format option, and check it is creating a RAW1 partition on C, if the drive letter is different, restart the PC and it should default to C
The purists will say that it is impossible to make data non recoverable on a useable hard drive, that said, if you shred files, recovering them will take more work than most people will want to put in