I have a pretty good G4 digital audio powermac but am finding the 533mhz processor a bit inadequate these days. I obviously want to upgrade but can't afford to buy new, so was thinking of a 2nd hand processor from a more recent machine. The only problem is that I don't know what processors are compatible with my machine. (i would like minimum of dual 833mhz) Can anyone help? Does anyone know where i could buy one?