well ive mapped in cod 2 , this is how i do it.
1) first create your skybox.(if you dont know how to do this read a tutorial.)
2) Press esc to deselct your brushes.
3) Select one side of your skybox (top, bottom, or a side)
4) Press N to bring up the entity box.
5) It should pop up on worldspawn. If not you havent followed the instructions you must have done it wrong..
6) On modsonline there is a tutorial on the worldspawn settings. Simply add the values and keys, and find the settings that are right for your map.
7) add your spawns and an intermission.

i think thats it