Leopard OS X restore to a Powerbook G5?

Okay - I restored my Powerbook G4 to factory settings because I was giving it to my mother and I was taking her iMac. When purchased, my Powerbook G4 came with Tiger OS. A couple of years ago, a friend with an extra copy of Leopard OS X, let me install it onto my laptop. I did a complete backup to an external hard drive before I restored the Powerbook. Obviously, when I go onto the Powerbook now, it is back to Tiger OS. The problem now is that Migration Assistant with Tiger OS does not offer the option to connect to an external hard drive to transfer all of your data back. What I'm wondering is, is a .dmg or some sort of copy of Leopard OS in any of the external hard drive data that was on my Powerbook prior to the restore? If not, can anyone offer any suggestions? Yes, I know I can purchase Leopard OS X on ebay or somewhere else and just be done with it but I'm trying to avoid that at the moment. Thanks.