No idea about the encrypting files part, but 2.2 can be jailbroken, if you have the first gen Touch (the ones with no external volume controls). It's the second gen Touch that can't be jailbroken yet.
You can put a passcode lock on the device as a whole. If you use Air Sharing to store files of various kinds, you can independently password protect that content.
Thank you very much for your answers.
My iPod Touch is 2G. So i have to wait for the new jailbreak version.
And password for the device is a useful tool, but I am looking for a solution for hiding or encyrpting individual files.