This is a troll thread right? If it's not then if you want to use a 7970 get a Mac Pro or PC.
It is not a troll thread, the linux drivers should be able to initialize the 7970 just like an unflashed 7970 will work in a mac pro in windows. It would work in OS X, and it does, on the mac pro, but only in 10.8, 10.5 has no recent AMD drivers, but linux has loads.
The only you will get it to work is to find a PPC bios for the 7970 and flash, and i'm fairly certain that a ppc bios doesn't exist for any card past the 7800 GTX. At least not publicly anyways.
Who has and creates roms? Is it AMD, or their subvendors?
Apple doesn't have 10.7 or 10.8 running on G4/G5 PowerPC type machine or even have the source complied for that because it would be extremely slow, even on the pompous quad. Because of 10.7 and 10.8's 64-bit requirement, it would be limited to G5s. But because of the G5's high overhead when running a 64-bit binary, it would be extremely slow. Much slower than an early Core2Duo running the same 64-bit binary. This slowness and Apple's push to make 10.6 a 64-bit native OS caused it to be dropped from PowerPC machines. Not Apple's greediness or to make people buy a new machine, but because it would run slow on G5's. It is very likely that it would run faster on a 1.8Ghz G4 than a 1.8Ghz G5 because of the G5's 64-bit overhead.
This is pure speculation, but i would assume if anyone had them it would be Apple. AMD has no reason to create a BIOS for PPC hardware unless someone requested it specifically. The only reason Apple would request one is if they decided to go back to IBM. Although it's unlikely, i'm sure they have 10.8 running on PPC hardware for a just in case scenario, as well as ARM and who know how many other architectures. They would need a GPU to go along with those architectures.
If any of that is true, then getting apple to release that BIOS is probably not going to happen, but i wont say it's impossible.
Apple doesn't have 10.7 or 10.8 running on G4/G5 PowerPC type machine or even have the source complied for that because it would be extremely slow, even on the pompous quad. Because of 10.7 and 10.8's 64-bit requirement, it would be limited to G5s. But because of the G5's high overhead when running a 64-bit binary, it would be extremely slow. Much slower than an early Core2Duo running the same 64-bit binary. This slowness and Apple's push to make 10.6 a 64-bit native OS caused it to be dropped from PowerPC machines. Not Apple's greediness or to make people buy a new machine, but because it would run slow on G5's. It is very likely that it would run faster on a 1.8Ghz G4 than a 1.8Ghz G5 because of the G5's 64-bit overhead.
In benchmarks a Quad benchmarks as high as a 2009 MBP.
Apple doesn't waste resources porting OS's to PPC hardware 7 years after it was abandoned, or even the current version POWER chips. They're a multi-billion dollar corporation who makes mostly very intelligent decisions. I wouldn't doubt they have someone working on ports to ARM, however, just to see how viable it would be to manufacture their own CPU's.
You don't think apple wants to futureproof OS X? They probably have OS X running on every architecture imaginable.
In benchmarks a Quad benchmarks as high as a 2009 MBP.