This evening I had to get a copy of Infopath 2007 on a notebook to run a toolkit that MS provides.
Unfortunately I used a key that had been used before, and activation was rejected. It was a simple mistake, and it turns out, easily corrected.
Rather than uninstalling and reinstalling using the proper key, just go to this article and delete a couple of registry keys. The next time you run an Office program, you’ll be prompted again for a product key. Simple and fast!