I'd rather not detail all the issues about this, but will share the solution.
Install 2 parallel installs of Windows. You'll end up with a BOOT MENU to select which copy to run. Install one version in one OS and another in the copy.
The reasons for this are simple, but I'd rather not discuss it.
I work in a Mac environment but I also have a Windows machine at home and sometimes they ask me Windows questions. My boss wanted to know if you could install a later version of PowerPoint on a Windows machine that already has a version installed , or if it will overwrite the earlier version. I really don't know. Can someone tell me or give a link to the info?