If you wanna play in DC-Final, install to that directory
eg: C:\Program Files\EA GAMES\Battlefield 1942\Mods\DC_Final\Archives\BF1942\levels

If you wanna play in Desert Combat (whatever version), install into that directory
eg: C:\Program Files\EA GAMES\Battlefield 1942\Mods\DesertCombat\Archives\bf1942\Levels

If you want both.....go for it!!!