Trucrypt does have a feature where you can have two different encrypted drives, each one protected by a different password. The first password is to an encrypted volume which looks encrypted (i.e. if you looked at the bytes you could tell there was structure, as with most actual data), and there you would place decoy files. Then if you enter a different password, it will mount a different encrypted volume, and this is written such a way that it is statistically no different than random bytes on an unused disk... undetectable (in and of itself anyway, there are many other things that can be done forensically to detect such a hidden volume not related to the volume itself).
I just don't like that they have pretty broad powers but little apparent accountability and it doesn't seem clear as to what a person's rights are and what the possibilities are.
Anyway, interesting read here about this going on in the US last year:
http://www.eff.org/deeplinks/2008/05...arches-while-t