Hello, I was wondering whether or not it's possible to use the same Snow Leopard CD on multiple macs and by that I mean the CD key. I've already used my Snow Leopard CD once on my Macbook Pro which now has Lion installed on it. Another and older Mac now needs to upgrade to Lion but it has to upgrade to Snow Leopard first. Do I have to buy another CD? Or can the other mac use the same CD/serial key and then upgrade straight to Lion? Thanks in advance.