Noel, the best way to go from 4 to 7 for projects is to create them from scratch in 7, using the assets from the old project. I personally believe the checking and correcting of upgraded projects (and you need indeed an intermediary step) takes much longer and causes much more frustrations.
Problem about having those versions on one laptop: I suppose a 'new' OS will be used as well, and it may not even be possible to install CP4. Only a few systems could have it on Win7 years ago, I was lucky with my laptop, but most users couldn't use it.