gdk-window-move (window x y)

window -- a gdk-window object
x -- a :int with the x coordinate relative to window's parent
y -- a :int with the y coordinate relative to window's parent

Repositions a window relative to its parent window. For toplevel windows, window managers may ignore or modify the move; you should probably use the function gtk-window-move on a gtk-window widget anyway, instead of using GDK functions. For child windows, the move will reliably succeed.

If you are also planning to resize the window, use the function gdk-window-move-resize to both move and resize simultaneously, for a nicer visual effect.