A friend just recently asked me if there was a way he could forge the properties of his hard-drive so that it would look like it had nothing on it. I told him it wasn't possible but now I'm thinking I could be wrong.
-alivingspirit
Theoretically, there's a bunch of different things you can do on a running system - but as soon as the disk is checked from a linux livecd, in another machine, (...) there's nothing you can do to mask the fact that there's stuff on the disk.
His best bet for safety would be
TrueCrypt, but that's probably more than he wants/needs, and has some problems of it's own