old pc
as a pc, the mac pro is a questionable choice. you can put any pc video card in it you want. however, doing so pretty much means it won't boot as a mac any more. kernel panic. wee. most video cards need more power than they can suck through the pci bus. neat huh? they need a more direct connection to the power supply. the mac makes this kinda difficult. video cards for mac come with a special cable that plugs in to the motherboard. video cards for pcs don't. wee. you can buy a proper cable for $30 on the internet. or you can buy a $3 cable from fry's. the mac pro's power supply is hidden away. i don't use the cd drive. so i unplugged it and used the $3 cable to connect the cd's power cord to the video card. wee. did i mention i bought a real life pc? wee. go apple. stick with the novelty appliances. play games in the cloud.