You guys are thinking of different things - there were the NewerTech iMaxPowr G4 upgrades, the PowerLogix iForce G4 upgrades, and the Sonnet HARMONi G3 upgrades (which included a FireWire port) available for tray load iMacs, the Rev. A and B Bondi iMacs (which had the Mezzanine slot), and the C and D "Fruit flavoured" iMacs (which had no Mezzanine slot). Regardless of their Mezzanine slot status, however, all tray load iMacs still had the CPU mounted on a daughtercard, making it possible for third parties to come up with processor upgrades.
The slot load iMac, however, had the CPU soldered directly to the logic board, and therefore apart from this iTechDV upgrade, there were no other processor upgrades made for the slot load iMacs.
Either way, great find!