Half-Life Cheats

Half-Life Sniper Mode with any weapon
If you have a crossbow, you can get sniper mode on any weapon, and here's how: Simply quick-save your game, go to the crossbow and zoom in, and then quick-load. When the game pops up again, you will be zoomed in on the weapon you had when you saved, and can cycle through the others as normal. To zoom out, just go back to the crossbow and press 2nd attack.
OR