I guess it may work, why? 1) MacPro's 2600XT works fine in PC, it has PC's bios. in iMacs 2600XT there is little efi part, which specifies driver (Hypoprion, there is string ATY,Hypoprion) but macpro's card has no such string in bios. so i guess it's simple PC's bios 2) 3870 works fine in MacOSX, there is full suport for it, even Sleep works. 3) 3870 works with same values in IOReg as 2600 (they come from boot.efi, via IODT:/efi/device-properties var) So, my guess, it may work if EFI driver will set keys for it. Anyone wanna try ? p.s. need to have 10.5.2 to try it.