Starting from
http://answers.unity3d.com/users/2664/davea.html

I (alain) jumped there by hazard :
http://answers.unity3d.com/questions/17676/guiwindow-resize-window.html

And tried the script ( OK , not from Dave, but to show what is "to share" :)

http://mixed3d.free.fr/dave/davemixedwindowPlayer.html