Yes, I've used two different PCI PC-flashed Radeon 7000s in my 9600. I think the 7000 is a good card to flash as most are of reference design.

The 9600 is picky about card placement; I recall the MACH-V based variant is even pickier. It takes some shuffling of cards to get things right sometimes. IIRC the top slot is bus-mastered and takes highest priority, so best for ATA/SATA/SCSI cards, and then the video card, next up things like FW/USB/lesser cards.

JB