Ones does not simply "decrypt" (MD5) hashes. It doesn't work like that. Unless you can magically reverse engineer the hash algorithm. In which case the integrity of the algorithm sucks or you're some super genius hacker.
You typically crack the hashes - usually through rainbow tables or generic database look-ups (which was the main way it was done on Gaia back then).
Well normally you can just decrypt MD5s unless they're salted or otherwise.