Helpful article, although my case is a little different. I have a second HD in my Mac, with Tiger already installed there. So it would (hopefully) just be a matter of reinstalling FCP on that drive. Of course, whenever you think something will be simple....
The only thing to consider is the that the "Pro Application Support" is different for Panther and Tiger. As long as you do a clean install and then use software updates to download the updates you will be fine.
don't use any old downloaded updates, use software updates.