Jaxz, check the sticky thread in the JavaScript section.
It's not possible to decrypt the code since it is encoded using a hash, which is a one-way encryption method, unless you try every possible passphrase combination.¨
It is however overkill to do this kind of encryption and it's really a false sense of security.
To be able to use this particular method, you must hand out a password to each user who is allowed to view the site. Each time something changes on the site, it must be reencrypted with that exact password allow visitors to see updates.
But once a legitimate visitor has the password, he/she can also access the complete source code and rip it all anyway, just like if you had password protected the folder in which the sensitive files are. With the password, one can still copy everything so you'd have to keep a very close eye on who you let in.
If you don't want your scripts to be stolen, don't put them online. As soon as the script is downloaded to the client for excecution, he's got the whole source, no matter if you encrypted it or not.