Hi NeHe :)... I Think That Will Be A Good Choice To Make A Selection Tutorial For OpenGL. As Many Game Writers Need To Find The Selected Object... Like Game Genres (RPG, Strategy ... ) Could You Write A Tutorial About Selection ? [Edited by - spider853 on January 7, 2008 6:34:14 AM]

There is a "Picking" tutorial as well as an article on the use of glUnProject.

First one being a lot more basic and possibly not much use to most 3D games. The second however more or less tells you how to convert screen coords into 3D coords in your 3D world. The only thing missing is the figuring out what those coordinates intersect with, by taking those coordinates and comparing it against the volume of the "hit boxes" of all the objects in your scene (or view frustum) to find what was selected.

I agree that it would be nice for a more complete tutorial to make it easier for people to learn something, that is very much required for any 3D game (and tools, apps, etc).