Ok so by the license agreement I couldn't, but it is possible to do it? I'm not saying I'm going to do this because Apple has me by the balls waiting to hear about the processor bump for the macbook Nov 6th (Leopard on my iMac is going to have to hold me over for a while!) But there isn't an activation process like Microsuck?
With a Leopard DVD, there is no activation of any sort...just install and you are good to go. On the other hand, the iMac or Macbook Pro DVD's that came with your computer can only be used for an iMac or Macbook Pro respectively. Not sure if you were asking this, but thought I would throw it in anways!!