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.
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