I appreciate the info and input, burning the install files to a DVD worked for whatever reason. I would be curious, but not curious enough to do it on my own, to see if I could duplicate the issue in reverse. i.e. Cancel the install from the DVD then install from an external drive.
So far Windows 7 seems nice but I do find it a bit disconcerting that wiping the current install of my OS is recommended just because I had to to cancel out of set up when I was prompted to do so by the software. If it really is just a reg key, as Ken suggested, then it should be easy enough to delete the entry and go about my day.