Eyefinity PCI Express card with Apple Thunderbolt Display
You'll need a graphics card that can output Thunderbolt (if such things exist, I have not checked). The Apple Thunderbolt Display can only accept input in the form of a Thunderbolt signal, Mini DisplayPort will not work.

Apple does sell a Mini DisplayPort variant of their 27" display, so if you don't yet have the display you should get that instead