GUI and Mouse Input

Is mouse control implemented on GUIs yet? By looking some old posts I managed to do it for T2DObjects, but I have no idea how to do the same for GUIs. Any ideas on how to do it?

See this post for reference:
http://www.garagegames.com/mg/forums/result.thread.php?qt=56898

Thanks in advance

edit:
Just to clarify:
The basic functionality I want is onLeftClick, onRightClick, onHoverIn, onHoverOut, etc...