When you enter Quake 3 go to - Quake III Arena
When you enter Quake 3 go to the console
and type devmap and then what map you want to play on.
When it loads,somewhere it must say cheats are enabled.
When you start playing go to the console again and then type ALL of the following text:
give grappling hook
give quad damage
give battle suit.
If you type in all of these,then you will be invincible!!!
Plus if you type in the same cheat over and over again just by pressing the up arrow key and then enter lots of times then you will have the cheat for a long time,but dont do this with the god cheat because it might not work.