move the camera between the player and the mouse

I had a slight change of plans. I want to try setup an aim system that disregards height, or any geometry (basicly you just shoot straight from the gun, no pitch). I think that Line Plane Intersection you spoke of might be what I’m looking for.
I tried getting it to work myself, but didn’t get any favorable result.
I’m not sure how comprehensive it is, but if you could give me a pointer that would be greatly appreciated!