Two more notes I picked up from the thread I linked:

-the CPU literally only has to be the cheapest to fit your motherboard, it is NOT needed.
-RAM for BTC mining requires 2GB, for LTC mining 8GB (worst case)
-cooling is VERY important, make sure the version of the 7950s you are selecting have HEAPS of cooling (the gigabyte model I selected has three fans) and get some big, high-rate, NON-silent fans into the case