Apartments are rented with the expectation that things will be hung on the wall, etc. Two toggle bolts in the ceiling and two holes is enough to mount a projector firmly. About 5 minutes and some spackle is all it takes to repair the holes. In my old apartment I put up a plasma (4 holes) screen (6 holes), and projector (2 holes) - and my total fine for these holes? $0.00! It is just standard when renting an apartment, that when you move out, they patch and paint. It's quick and easy and not expensive.
If you really want to shelf mount, then you really have to consider the projector you get...
1. Projectors can't be placed wherever you want. Like the zoom on a camera you can only get to close, or so far away, if you want the image to fill the screen.
2. If the projector doesn't have lens shift, than it must be placed a certain amount above or below the centerline of the screen. Many cheaper projectors this amounts to 1-2 feet above the TOP (or below the bottom) edge of the screen for a 100" diagonal screen.
If I were you, I would get a Sanyo Z4 or Panny AE900 and then put it on a shelf. The Z4 has WAY more lens shift which means you can put it almost anywhere on the rear wall without any issues at all (if the distance is right). Both projectors have 2x zoom lenses which is a huge range for projectors, most are about 1.2x or 1.3x zoom. So, for a 100" diagonal, you can put either projector between (ABOUT!) 10 and 20 feet from the screen.
Very cool.
