Area 51

Be an Alien from Jim Kelley
shot nothing but the staar team, you will have to shot about four blue staar team people for it to work.

Secret Rooms from Jimmy Wiggler
Level 2(Hanger) - Shoot out all of the upper windows of the far back wall in the Hanger in order to enter the 'chow palace'.
Level 2(Hanger) - To enter the Egg-cellent Room, make sure that all of the yellow barrels are shot while riding the forklift before you get to the parked trucks
Level 4 (Airport) - Make sure that every yellow box is shot while riding in the STAAR jeep to enter the X-Marks the Spot Room.
Level 5 (Office) - Shoot the door-plate of the second door (marked General Weatherby) as the door is opening to the access the Headquarters Room.
Level 7 (Abandoned Base) - Shoot all of the yellow barrels at the first area where four purple zombies are throwing barrels on the hill to access the Chow Palace, again.
Level 8 (Mothership) - Make sure that all of the panels are shot off of the mothership before it escapes to get the good ending. If the mothership escapes without having all the panels shot off, the bad ending will be revealed.

Secret Area from ShowBob
In the right half of the 6th level (The Main Control Building).... if you shoot out all of the computer moniters, you can go to the Egg-Celent secret room.

Secret Area from Tom Moscato
Airport Level (4) shoot the cockpit windows of the 747 out to get to a bathroom where the aliens are using the urinals