You will have to use an appropriate Mac compatible video card (a.k.a. You can't simply install a PC based solution. How much is your budget? Keep in mind that Mac GPUs tend to cost quite a bit more than PC GPUs of the same model family. I also assume you want a new GPU at least as capable (likely more so) than the GPU you currently have. BTW, does your current GPU still work properly?
I DO NOT RECOMMEND any available GPUs that have been 'flashed' from the PC version to the Mac version. They almost NEVER fully work properly. Please clarify. In the meantime, this is a very nice Mac GPU.