Encryption Software

Truecrypt is released under the GPL (General Public Licence), meaning it is free to download and use without restriction.  You can get it here: http://www.truecrypt.org/downloads.php

The documentation is available online here: http://www.truecrypt.org/docs/

A quick scan of online reviews suggests that it is well worthwhile reading the documentation, as this comprehensive package has lots of options and lots of ability, so it would be wise to learn how to use it, lest one encrypts one's data and promptly forgets the password.