MacBook Pro not booting from CCC clone from earlier MacBook

Hey, all

A bit convoluted, but here's the deal.

My wife bought a MacBook (back in 2009, the aluminum model WITHOUT firewire). She got a new job that gave her a MBP that she can take home and do with as she pleases. We decided to clone her MacBook's drive (was, at the time, running 10.5.7) to an external drive (USB 2) and wipe the MacBook to give to her folks as a gift.

Long short, her MBP wouldn't boot to the external drive; my MacBook (same model as the one we cloned) did it just fine. I figured since her new MBP came with Snow Leopard, I should upgrade the cloned OS so the BIOSes would match up. I upgraded the cloned OS to the current version of 10.6, still no luck. Again, it still boots up on my MacBook just fine, but not my wife's MBP. I even created a partition on her internal drive and recloned the drive to it; I still get the same thing: chime, grey apple on white background...hang. It never progresses beyond that, and it just sits like that for hours until I reboot to her "work" drive.

I'm kind of at a loss, and don't really know how to fix this; I was hoping to make this easy for my wife so she can have her work and personal computers on different partitions of the same internal drive.

Any suggestions? The MBP is 3 months old, but was factory new. The MacBook is a mid-2009 model, aluminum, user-replaceable battery, no firewire.

Any help would rule. Thanks!