Area 51 Cheats

In the level "The Grays" proceed into the 4th room in the level, where you can see the monorail you entered the level from out the window. Push the computer console there and it will say "Lifter activated". Make your way back outside to the monorail, you can now stand on it. Run all the way to the back of it and you will be warped to a weird room with sharks that have machine guns attached to their heads.

On the HOT ZONE mission at the beginning of the level.Hidden in a corner there is the original AREA 51 arcade game complete with red and blue lasar-light guns.