I think if Leopard came with your MBP, it won't work with the iMac anyway. If you bought Leopard on its own, it would work. However, it would still be a violation of the EULA. For any other OS upgrade it would be different since they didn't have upgrade pricing, but since you're getting it cheaper since you already have Leopard, it wouldn't be within the EULA to install that same Leopard on a different computer. However, if you bought the Mac Box Set, it would be a different story, as that doesn't have Leopard upgrade pricing.