File:kaa_widgets.py----------------------------------------------------
#SEE : http://unpythonic.blogspot.com/2007/03/custom-pygtk-widgets-in-glade3.html
import gtk
class SearchPanel(gtk.ScrolledWindow):
    pass

print 'IS IMPORTED'

File:kaa_widgets.xml----------------------
<glade-catalog name="kaa_widgets" library="kaa_widgets" domain="glade-3" depends="gtk+" language="python">
    <glade-widget-classes>
            <glade-widget-class title="Search Panel" name="SearchPanel" />
    </glade-widget-classes>


    <glade-widget-group name="kaa_widgets" title="kaa_widgets">
            <glade-widget-class-ref name="SearchPanel"/>
    </glade-widget-group>	 

</glade-catalog>

--Result of starting glade-3 -------------
** (glade-3:16537): WARNING **: Unable to load icon for GtkMenuShell (Failed to open file '/usr/share/glade3/pixmaps/22x22/menushell.png': No such file or directory)

** (glade-3:16537): WARNING **: Unable to load icon for GtkMenuShell (Failed to open file '/usr/share/glade3/pixmaps/16x16/menushell.png': No such file or directory)
IS IMPORTED

** (glade-3:16537): WARNING **: We could not find the symbol "search_panel_get_type"

** (glade-3:16537): WARNING **: Could not get the type from "SearchPanel"

** (glade-3:16537): WARNING **: Failed to load the GType for 'SearchPanel'

** (glade-3:16537): WARNING **: Tried to include undefined widget class 'SearchPanel' in a widget group
** Message: No DevHelp installed on your system, devhelp feature will be disabled.