My puny 250 GB iMac hard drive was full! Only 5% resources were left free which slowed my beloved iMac to a crawl. I could not upgrade to Mountain Lion because I didn't have the space.
After watching your repair video, I decided to try the upgrade. I also purchased the new 2 TB hard drive, a couple of heavy duty suction cups and a couple of plastic spudgers . Once I figured out how to clone my original hard drive, the swap went almost flawlessly (I did manage to lose 1 small screw...doh).
Would recommend purchasing a Universal Drive Adapter from ifixit.com to clone your original drive ($29.95). My only local option was to purchase a single hot swappable rig that cost me another $49.99 plus tax. I will probably use this rig once, since it is usable on SATA drives.