Not the best day. I went to plug my G4 into my iMac to transfer some data. After I booted the old machine using the "T" key, I noticed it wasn't working. THEN I noticed my external firewire drive on my iMac had gone off. A few minutes later I noticed a burning smell coming out of my iMac. Finally, I realized the G4 has a sweet little feature that lets you plug in a firewire cable either way, and I had mistakenly plugged it in the wrong way.
End result... one firewire port on my iMac is dead. The other one is acting strange enough not to be usable (disappearing and empty folders). So, I fried the firewire ports. Sigh.
Are these on the motherboard, as they are on the G4? If so, it's not worth fixing, as I might as well just find some extra money and get a new one once Leopard comes out.