I want to make a 3d shooter. how can i put a image on the screen that it will look like a weapon? Sig

If you are programming a 3d shooter you should already know how to do something like that... For Doom they just superimposed a sprite on the screen. Newer games use actual 3d models positioned slightly out in front of the camera.

Almost all games excluding Q3 use different models for the on screen weapons and the ones on the ground(or whatever), maybe to get a little speed, only modelin what will be seen, but if your doing a multiplayer I think it will be very hard 2 use sprites as weapons, as how will they see the weapon, u know? whateva, later(jus tellin, i not dat far in my shooter)