yes, what IIIaas said. older computers may not give you enough "juice" to get the job done, especially plugged into a hub, keyboard, etc. Also Apple's external dvd drive meant for the Macbook Air etc, will Not work with a mac pro---without a hack (which I can't remember at the moment). if memory serves me, those dvd drives are ATAPI/IDE, which are getting pretty hard to find. However, you can replace them yourself, which I know is off-topic. You can buy a sata dvd drive, plus an atapi/sata bridge which fits onto the back of the dvd drive itself, and then install the whole thing into your Mac Pro. all you'd need is a small Phillips screwdriver and a little time
oh well
John b