[lug] drive free space "wiper" recommendation

[karl horlen]

i need to ship a computer back that's under warranty. i've already moved / deleted the files off of the drive that i deemed sensitive.  th

can anybody recommend a good, free, non spyware based utility to help me "wipe" the free space left by my previous deletes and moves?  dban looks like an *entire* drive wipe utility.  i don't want to permanently delete the entire drive, just the unused space.

fyi, this is a win xp based system.

thanks