On the level Reliance where you play the flashback (the snow level) well when you sneak around the base thing and find a way in, look in all the rooms knocking out the guards with your tranquillizer gun.
In one of the rooms there is an arcade machine a guard is playing on, theres also another guard in the room, shoot both of them and press action on the arcade machine, you will be able to play an arcade game called Earth Impact.
Even better is that even after you have completed this level but feel like playing that game again you can press start and go into Applicants (the computer icon) then click on the rock icon to play the game anywhere you want in any level you want.
Although this is not a good idea in the middle of a fight.
On Certian missions in the past ( NOT preperation), if you fail you get a different ending where you appear in an interrogation room (the same one as in the first level, isolation) and a mysterious voice talks to you and somehow helps you.
P.S. i have only got up to the level past reliance so i only so far got them on reliance and feild work)
FIELD WORK: shoot a member of winter ice team and kill them.
RELIANCE: Get seen by a guard in the first building and get a fire fight started, DONT help the commander, let him die!!
Correction: By Smurfkiller
In the tip it says that it does not work in the level Preperation. That's not true. If, on the beginning of the Preperation test in which you have to make it to the compund gates tranqing all the guards, you backtrack from the beginning you can find an arms locker. In the locker is an assault rifle. If you kill a bunch of guards with the assault rifle, then die, it gives you a failure movie.
In the 1st asylum level, in the section with the rooms near the CCTV control room, find and enter the storeroom which contains a tranquiliser gun, some boxes and shelves. Use telekinesis to get an item off the top of the shelf on the left. It's a disk. Now go to any of the PCs in the level and click the disk icon on the desktop and you can play X Space '92. It also saves to your applications menu, like the Earth Impact game!