Here is my first attempt at this lark.
I went for the windows forms methodology as for my next attempt I'll be adding in a few other controls to act as option menus etc, and the nice easy windows forms environment seems much friendlier to me at the moment than the mysterious world of the dark GDK.
but for now - The Moveable Cube does the standard 3d spinning cube. but will now move to your mouse position whenever you click on the game screen.
this is uber basic, but I found it very useful in aiding my own learning curve. Hopefully it will be of some use to others as well
source code is attached (.net 2.0)