9600 Pro To XT?

Is it possible to put a 9600XT bios onto a Sapphire Radeon 9600 Pro 128MB Atlantis?

no, they use different cores: rv350 for the pro and rv360 for the xt

besides that, i wouldn't risk overclocking the pro core to 500mhz, which is xt's stock speed

It's possible. I'm not sure about teh 9600's, but the 9800 Pros can can come with either the R350 (Pro/NP) or R360 (XT) core, and the only way to tell is to take the HSF off. If your 9600 has an RV360 core and you can run it at XT speeds (not sure what the clocks on the 9600 XT are) then the flash should work.