Can you use any intel processor? Reason why I ask is because that instructions call for the Intel Core 2 Quad Q9650 3.0GHz 12MB L2 Cache LGA 775 95W Quad-Core Processor which sells for $324, but I would be happy with this one:
Intel Core 2 Quad Q9550 Yorkfield 2.83GHz 12MB L2 Cache LGA 775 95W Quad-Core Processor $259

And can you use other motherboards or do they use what's on that list because of OSX?

Was curious...looking for a motherboard that you could put 2 processors on but can't seem to find them.