I rendered a few polys onscreen, and to select them I need the 2d points/field that the 3d poly takes up on the 2d screen. Beleive me GL selection buffer and RGB selection have failed for me I have tried them. Very much appreciate help.
Take a look at the following discussion, it may have what you are looking for
http://www.opengl.org/discussion_boards/ubb/Forum3/HTML/000613.html