[Dave]

The user's password is hashed, not encrypted. This means that it only goes one way, you cannot get the hash back to plain-text aside from brute forcing it or knowing the original value. (Which only the user knows)

If you want to use encryption so the data in the database is not shown as plain-text and you need the ability to decrypt it, you can do something like this: http://thinkdiff.net/mysql/encrypt-m...es-techniques/ but will require a bunch of modifications to the core files.