Mini Game - Earth Impact:
This Minigame is "hidden" in the Reliance level.
After you entered the building through the vents there is a room with guards and 
Arcade machines inside.
Kill the guard playing one of the Arcades and use the Arcade he was playing.

Once you unlocked this Minigame you can always play it through the Pause-Screen!

Mini Game - X Space '92:
This Minigame is hidden in the Madness level.
It's located up on a shelf in a room that has only one entrance an no connection to 
the other rooms and a camera above the door and a guard in front of the door.
The room is before the third checkpoint which is the fenced door that needs a 
keycode to open. 
The room is the storage room.
When you're in the room use your Telekinesis to get this game. When you have it 
use it with any computer in this level to play X-Space '92.

Once you unlocked this Minigame you can always play it through the Pause-Screen!