Half-Life: Game Of The Year Edition Cheats

Enable the impulse 101, impulse 105,
and notarget codes and get the Magnum. Walk up to a scientist
from behind, then shoot him in the back of the head. Certain ones
will make a noise, stand for about five to ten seconds, then fall
and die.

Get the HEV suit and enable the impulse 101, impulse 105, and notarget codes. Reactivate the cheat screen, and keep using the impulse 101 code until your HEV suit is full. Choose the high explosive (press 5 twice) and return to the lobby in Sector C Test Labs, where the security officer is on the computer. Go behind the desk and throw a high explosive under the desk. Walk anywhere you want, but not past the loading point, then detonate it. Walk back and the security officer should be on the desk. Talk to him.