Some additions,

In this forum I often come across the problem that people want to move their player to where they click in the 3d-world. The solution to this is - as mentioned very often - the mouse_to_level funtion in the templates.
I do not think that I can fix my problem that way, but perhaps someone knows better than me?!

Another thing I want to do is give my 3d-pointer some lines (along the 3 axis) to better know where it is in the 3d-world.
Has someone an idea of how to best do that? Is D3D the way to go? (btw I do everything (event handling, movement, ...) in dll's)
I recently stumbled across a built in function of 3DGS: when pressing the d key a panel with some information shows up. Pressing d again some red lines along the room borders show up. Where is this implemented? These lines from my pointer to the walls would exactly what I want to do.

Ok so long and if anybody has accomplished such an 3D pointer - please let me know.