I upgraded the internal drive in my old powerbook and instead of reinstalling OS X and copying everything back over, I put the old drive in an external enclosure, booted off the setup disk, went to disk utility, restore tab. I selected the new drive as the destination drive, and the old one as the source. It took a little while to copy everything over, but once it was done, I rebooted and it started up as if i hadn't done anything at all. Only difference was 40 more gig's of free space. disk utility didn't even care that the 2 drives were different sizes.