Projecting DLP from the rear of the screen

What are the benefits of rear vs. front projection?

If I want to project from the rear, how far does the projector need to be from the screen? (Assuming I want a 72- 80 in 16:9) If I use a mirror to reflect the image, do I count the distance from projector to mirror, mirror to screen to get the total distance?
humphry has a distance calc for every projector. is the forum to ask that question about using a mirror

projo model, etc.

There are rear projection setups available from most major screen mfgs. Call one up.

Some projectors can accept different lenses to shorten throw for a given screen size.