How do I create a wall of green lasers?

You might get some ideas from this image search

It depends on the effect you want to achieve. If you just want to point the lasers to the floor you won’t see much, just the spots on the floor 1 inch apart. You normally will not see the beams unless there is something to catch the light like talc in the air (bad to breathe though). If you want stripes down the wall you will need to optically convert the beam from a point to a line. In any case, yes, individual lasers will be the way to go, and aiming them precisely will be a pain. You might do better to construct and project a single image such as this:
http://upload.wikimedia.org/wikipedia/commons/1/1f/Green_grid_for_McCollough_effect.png
Which could be done cheaply with something as simple as an old fashioned slide projector.