Basically you need the card to be flashed with a Mac ROM.

One of the sticking points is that the mac ROM is often 128KB where as the PC one is 64KB; thus different size flash ROM chips are often used. Strangedogs.com is a good starting place but you may also find www.cubeowner.com useful.

I have a feeling the 7800GT has its drivers as part of Mac OS X 10.4—but I can't 100% assure that.

I have a flashed 'PC' Radeon 9800 Pro card in my G4; it works flawlessly consdering the 9800 Pro Mac & PC Edition is something like £200 inc. VAT; I now have more or less the same card (128MB VRAM, SVideo, VGA and DVI-I out) for a fraction of the cost.

As such, flashing a PC card is quite a good option in my book.

Vicky