I am creating a 3rd person shooter game in XNA. I have been searching everywhere to try and find out how to impliment a laser sight for my gun. This probably goes without explanation, but I basically want to have a laser that points to whatever I am shooting at. I also would like it to be such that I can add a glow and flicker to it. Any help?

This overview should get you close,

Create a cylinder with a small radius, modeled so that one end is at 000 and the other at 00,-1.   Use subtraction and Vector3.Distance to find the distance and direction from the end of the weapon to the target.  Scale the cylinder in the Z direction by the distance from the end of the gun to the target (createScale(1,1,Distance).  create a world matrix for the cylinder with the direction to the target as Forward and the end of the weapon as the position (Matrix.createWorld(direction,position,up).      Then, you can swap out textures each frame to create some type of animation on the texture, or if you're using your own shader the sky's the limit.

Best,
Byron

Thanks for the reply Byron. This may seem like a silly questions, but i'm not sure how to create the cylinder. Is this something I would do in Maya, and then export into my game, or can this be done directly in XNA?

Thanks

Technically it could be done in XNA, but the simplest route would be to do it with a 3d program (e.g., Maya), export to .x or .fbx & load it through the content manager.

Best,
Byron

You can also just stretch a billboarded quad from source to destination.

The main important bit is to find what the laser "hits" and only draw the quad until that point, because whatever it hits should shadow whatever is behind it.