Install GP3 once on your pc. Go to the directory in which GP3 was installed.
( C:\Program files\Microprose\Grand Prix 3 ) Copy the folder named Grand Prix 3 into this directory..... C:\Program Files\Microprose\. You should now have a new folder named Copy of Grand Prix 3. Change this folder name to GP3 1981 Season. (Or similar) You will not need to change any other folder names, just make sure that you start GP3 from one of the Grand Prix 3 folders. ( Grand Prix 3 or Grand Prix 3 1981 Season ).
Did it work ok? It worked ok for me! I have 8 folders in this directory! ( Grand Prix 3 1996 Season, Grand Prix 3 1997 Season.......