As I noted above, if current MacBook Pros could run OS X 10.5, they would almost certainly require an install disc of 10.5.7 or later, since that's the OS version they originally shipped with.
I suggest trying with a 10.5.8 disc or bootable clone if possible. (Emphasis added)
I guess your post reinforces that.
As I said, I don't really hold out much hope that it will run, but slolerner is so adamant, that it's certainly worth a try...nothing like a bit of empirical evidence to reinforce dogma.