Vista - .MPQ files diablo II and starcraft

hello i am trying to run two different games, Diablo II, and starcraft both with out the cd's, blizzard tells you to take the .MPQ files from the cd and place it to the folder you downloaded the game, so i did that to both games and its fine the games work, but the problem is i cant set one .MPQ file to open for starcraft and the other.MPQ file to open for diablo. i can only have one .MPQ file open to one game at a time (so both icons would open the same game), i would be able to change it so they each open there own game but the "Always use the selected program to open this kind of file" is checked and grayed out so i cant change it for only one file.

any suggestions to uncheck that box?