Unable to reboot from USB on Snow Leopard I have an external hard disk, where I had stored my 10.5.8 image. The laptop had issues with keyboard and display, so I stopped using it. I have a relatively new(5 months old) Snow Leopard Mac book Pro.I also have a mini mac. When I reboot the mac mini with the 10.5.8 image, it works fine. But with MBP, when I reboot, it sits at the apple image and does nothing.

The image was created using SuperDuper. I basically have an option in superduper to copy the hard disk to a usb. I think it blindly copie the files.
It's because your new MBP has few hardware components that are not supported by Mac OS X 10.5.8. Just to be sure you can check where 10.5.8 chocking when booting MBP if you press and hold cmd+v during boot.