I simply ran out of space on the original 160 GB drive.
The repair went very well once I selected and cloned the new hard drive. The Seagate Hybrid drives sounded great, but after researching the Internet and finding a large number of negative reviews, I jumped to a Western Digital 750 GB, 7200 RPM Drive (Scorpio Black). I have TechTool Pro 6 which has a cloning tool in it. I tried it and was sorry. The first time, I had the nerve to leave it after it was about 50% done only to come back and find that my computer had been rebooted with out completing the clone. I tried again and after two and a half hours the cloning was done. Upon checking the computer with the new external cloned drive all the files that were suposed to be invisable were now visable. I erased the new drive, downloaded SuperDuper! and cloned the new drive without any problems at all. I assighned a space in the sorting tray for each step in the repair guide. As a result the reassembly was problem free. The computer works perfectly and the drive is wisper quite, with no detectable vibration.
I used the following guides:
"MacBook Pro 15" Core 2 Duo Models A1226 and A1260 Hard Drive Replacement".
"Importent Instructions for setting up your new hard drive". I really had a hard time finding this one!!
Stick with SuperDuper! Its free and it works perfetly. I was so impressed that if paid for the full version.