Partition Removed / File Recovery

I recently upgraded to a larger hard drive for my laptop, after dutifully backing-up virtually every file I had onto compact disks. While reformatting the new drive with the new O/S, I inadvertently made the mistake of keeping my old hard drive attached to the computer (via an external hard drive enclosure) - and when prompted during the reformatting process I agreed (stupidly) to the installation request to remove the existing partition from the old hard drive (obscure/unfamiliar drive letters the OS referenced is my only lame excuse here). Up until that point the drive had been intact, and was bootable, or at a minimum, could be read by virtually any computer via the external hard drive enclosure connection. Now I'm not able to read the drive at all.

Since I'm posting this, obviously I was able to complete the new hard drive upgrade successfully - but there were a couple of super-large files on my old hard drive that I was not able to easily get onto the back-up set of compact disks, along with my most recent bookmarks file - and a couple of other files, that I would like to recover, if possible.

I know that the existing files and file structure all still exist on the old hard drive, since only the partition was removed, and at least I didn't make the mistake of reformatting the old hard drive - so all those files are still essentially intact on the old hard drive. I've thought of a couple approaches to recovering those files, but before I do anything, I thought I would draw on the collective knowledge of everyone for some suggestions first. Ideas?