In truecrypt, the volume would report 2GB, not 512MB, and you have to be careful not to put in more than the invisible limit, otherwise the hidden portion will be corrupted/overwritten.
Truecrypt can have hidden volumes, the truecrypt file may be split into 1.5gb / 0.5gb. The truecrypt file reports 2GB, but different passwords mount different the different sized volumes, hence putting in the 512MB password will mount a 512MB volume of a 2GB file.
It works the way the parent says, not the way you say.
Oh, my bad then. I guess I should look at my volumes closer. :)