Phone went - just finished - a bit of an abrupt reply!
http://www.truecrypt.org/docs/
basically you have two options - encrypt files - store on USB
or the one I use
create a virtual disk
the app is completely self contained - so once you install it - the files can be copied wherever you want so on the usb - copy the prog files
create a virtual disk fo almost fill the space (leave 10 Mb or so)
then store your files in the virtual disk
this option is easier - but if something goes wrong you loose the disk - and all the files.
individual files are a pain - but you shouldn't loose everything.
gmail will allow single files up to (i think now) 20Gb
so if you e-mail the file for the virtual disk to yourself - you have an easily accessable backup - just in case you loose the key.