If your old OS drive is not encrypted then I think the easiest solution is to:
1. Drop your family member in hot coals (ok just kidding on this one
2. Install windows 7 on another drive
3. Attach your old os drive as a secondary drive
4. Take ownership of all files and folders on the old OS drive
5. Manually copy all important data to the new installation
6. Reformat old OS drive and use it as your new spare data drive
Before you go ahead, lets make a list of all the stuff that you need to copy so that we can check it over and ensure that nothing is missed.
- Documents from all users my documents folders
- Game Saves and high scores
RE Greg's solutions
- Using a boot disk such as paragon will also work for recovery
- Greg said "It makes it much harder to repair if Windows 7 is somehow not marked Active any longer" and these are wise words. It is possible to remark your old installation as active and move all the files over' but you don't know exactly what your family member has done. Therefore you're really risking all sorts of corruption, such as missing data, programs not working, databases not up to date (e.g. icon cache, WMI, WMP etc) that may require hours of work later to fix and that's if it can be fixed. I believe that the solution of least resistance (i.e. neatest, safest, and quickest) is a fresh install and data import.
Of course please let us know first if your drive was encrypted as you'll need the encryption key to recover data and the process is a little more involved.
Which ever way you go, we'll be here to help.