The hack worked for the FX5200 on the G4 iMac, I was hoping it would work on the G5. Thanks for the confirmation.
And no, it doesn't void the warranty. It's a software hack. It just enables what's already built-in, but disabled. It's easily reversible, and if something were to happen, there would be no way Apple could tell.
(just thought I'd get that out of the way before someone else starts unintentionally giving FUD)