I installed Leopard on a FireWire drive to test it before upgrading my MacBook Pro's internal Tiger installation. Satisfied with the results, I tried to use Carbon Copy Cloner to copy Leopard to my MacBook Pro's internal drive, only to find the external image was slightly too large for the internal.
Not wanting to spend $35 on iPartition, I dug around and found the GParted LiveCD. It provides the GParted GUI front-end to parted (a GNU partitioning program) on a live Linux CD. I burned the image in Disk Utility and booted up on it. Once loaded, it provided a screen to select which kernel version to boot up, even providing a MacBook option. At first it only recognized my internal drive, ignoring my FireWire drives. I unplugged my Leopard FireWire drive, and reconnected it using USB ... voilá, the software recognized it.
I've tried booting from the resized drive and have verified it successfully resized ...