Sorry I'm sure this has been asked a million times. Picked up a used first gen mac pro and it's come with tiger but he had lost the disk. I want to either install leopard or better still snow leopard or worst case just give it a fresh install. I'm just confused as to what I need to buy?, I've seen leopard for around £90 and snow leopard for £30 and well over £100 as a package of which I only want the os. Can anyone confirm which would and would not work on my machine? Will the £30 snow leopard work?