You don't HAVE to upgrade the cpu to use the new card, because AMD's latest flagship graphic card, the Radeon 7970, is the world's first PCIe 3.0 graphic card. Initial reviews suggest that the new interface would not improve graphic performance compared to earlier PCIe 2.0, which is still under-utilized. However, the new interface would prove advantageous when used for general purpose computing with technologies like OpenCL and C++ AMP.
So, if you don't have to and based on the above information do you still want to? I would however, upgrade to win 7 lol As well as getting an SSD or 2 to go along with that awesome card.