[gtkmm] Wrapping label at a given pixel?

[Maurizio Colucci <seguso forever tin it>]

Hello,

I must render a label wrapping after N pixels. (N is known) Is it possible?
I can't understand why this doesn't this work... 

        mNameLabel = manage(new Label(lNormalizedText));
        Glib::RefPtr<Pango::Layout> lLayout = mNameLabel->get_layout();
        lLayout->set_width(100);
        lLayout->set_wrap(Pango::WRAP_WORD_CHAR);

I really need help... I beg you. :-)

Maurizio

PS: This is for a free program: http://segusoland.sourceforge.net  
(screenshots 
included)