Buy a WD Caviar Black 1TB drive and clone the Green drive to it. Put the Green drive in the external enclosure, and use it for backup. Put your old drive back in your computer so you can connect it to your SATA port, and use it from there. Put all your runtimes on your Black drive, and use your old drive for something else- like an internal backup. As you've discovered, backups are quite useful.

Don't forget to keep a couple images of your OS/Programs partition on a special partition of your various drives to make replacing a broken OS easy. Don't ever defragment your special image partitions, and don't move or copy the images, or they probably won't work.