>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.
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Jonathan