It didn't work on the unibody MacBook Pro; for some reason they 10.5.6 disk did not have the correct drivers for the computer, so when it got to the kext loading, it stops and reboots.
Thank you for clarifying that regarding the unibody, but since the OP does not have a unibody a 10.5.6 retail (or even a 10.5.4) retail should work fine then.