Here is a GtkBuilder-example, which works with my build (GtkBuilder is almost like Glade).

class MyWindow
def initialize
@gui = Gtk::Builder.new
@gui.add_from_file("gui/win_main.ui")
@gui.connect_signals(){|handler|method(handler)}

@window = @gui.get_object("window")
@window.show
end

def on_window_destroy
Gtk::main_quit
end
end