how to get handle of active window

Hi All,

Can anybody tell me how to get handle of the currently active window in 
Desktop let it be kde or Gnome. Is there any Xlib function to get the 
handle. One xwininfo command is there, but for it mouse click is required to 
get the window property. So is there any other command or API through which 
we can get the various property of the active window in the desktop.

Also through process table or descriptor can we identify what all windows 
are there?


Karthik