Finding A point on a Rendering Context?

Ok, simplifying my earlier question…

If I have a given point in space, how do I find out at what screen coordinates, OpenGL will render it?

Then, given a point on the rendering device, how do I construct a line that represents the line of sight through that point?

If I know these two things, I can do the rest.

  1. gluProject
  2. gluUnproject

Thank you very much ZbuffeR!

That works great!