Doom 3 Tips

lag busters
remember, sometimes people want to enjoy a game without the lag.try turning off the shadows. its just one more texture that your computer has to deal with.
maybe some of the ambiance is lost but for the most part it will not lag as much. also there are some great mods out there that are easy to install and the great thing about them is they give your walk/run speed, ammo and all your health an added boost.
check out they have some pretty cool mods from adding more gore to speeding up your game.