WW Guestbook

The internet world's changed considerably in the past 4-5 years. Don't think I'd use a guest book that was that old as it probably doesn't have captcha built in.

Even with captcha and post approval, guest books are still prime targets for porn spammers. Frankly, keeping them cleaned up is usaully more troulble than they're worth.

To your question though, somewhere there;s a routine that encrypts the entered password and compares it to the stored password. You need to figure out what encryption algorithm that routine is using.
Most likely, it's an MD5 Hash. Google can provide many code examples for converting to/from MD5.