If you want it to appear in the Colony game lists or Tutorial list, you need to set the DescBlock entry accordingly, and set the right prefix on the name of your dll.
So for a colony game, you might have something like this line in the beginning of main.cpp:
SDescBlock DescBlock = { Colony, 6, 12, 0 }; // Important level details
Note the "Colony" constant. That's the important part.
Then you'd also name the dll with a "c" prefix. Like "cLevel.dll", only a more creative name than that.
For a tutorial level, maybe use somethign like:
SDescBlock DescBlock = { Tutorial, 6, 12, 0 }; // Important level details
and then prefix the dll with a "t". Like "tLevel.dll".
Oh, and as another note, you should keep the dll name short. Anything over 6 characters seems to cause problems with levels showing up more than once in the list.