Have you taped the pins on the PC flashed Radeon 9700 to get it to work @ AGP 4X?

http://themacelite.wikidot.com/flasher-s-buying-guide-9700

I've just flashed over a PC Radeon 9800 Pro for my MDD - taped pins but notice there is also a resistor removal mod to permanently force it to AGP 4X, which I'm considering.

The Radeon 9000 would have come from an MDD, it should work fine in a lesser G4 tower.  I'd clean the AGP slot out using electrical contact cleaner spray.