>Do you know if GNUPG can create a simulation of an encrypted Disk, like PGP Disk ?

If you're in windows (or linux), have a look at TrueCrypt (http://www.truecrypt.org/). It's able to mount encrypted volumes as drives, and supports a number of command line arguments, so you can write some scripts/batch files to do various tasks. It's also free open source!

It's not on-the-fly / per message encryption like PGP/GPG, but might suit your needs depending on how you do things.

--
Jonathan