Hi
I've got a P7P55D, i7 860, 8gb ram, W7 Pro 64bit, coolermaster 650w PSU
I'm upgrading from a 5850 to a 7870 - I've never had a problem upgrading a graphics card before.
I initially didn't bother deleting any drivers and just took out the 5850 and installed the 7870, booted up and all...