You shouldn't copy the MBR to a disk of a different size.
Norton Ghost sucks. It's incompatible with Vista+ in many cases.
Create a new partition on the 500GB disk, copy the *files* and not the image of the disk over (You can use an Ubuntu Live CD to do the copying, or hook both disks up to another PC and do it from there). Swap the old disk out and the new disk in, and follow our instructions on fixing the bootloader from here: Recovering the Vista Bootloader from the DVD - NeoSmart Technologies Wiki
Good luck. Let us know how it goes.