I want to make a projector show an image displayed on surfaces I would like to make a scene where a movie projector displays an image onto a wall but the image will get projected onto obstacles or even characters that pass between the projection wall and the projector. I have no clue how to accomplish this effect in Blender or even someway to do it in post. 

I don't even know if it is possible.
In your scene, add a lamp as the type spot.

With the lamp object selected go into the texture panel, under the lamp texture, add a texture with your image. You probably want to set Extension to Extend. Set the coordinates to object and input the lamp as the mapping object.



You can also set the spotlights shape to a square by ticking Sqare in the lamps settings.



Even overlapping projector lamps work.