I am working on my UI in directx8 and I have HUD drawing and my 3d world. I want to use the mouse to select units (3d RTS game). How do I get/create the 3d models screen space cordinates so I know what the mouse is clicking on in the world?

Oye... fun...

We were talking about doing that and kind of decided on ''dropping'' a line down the z-axis and checking sphere-to-line on the object.