Tk has already mouse wheel support, however, there is no binding in
perl/Tk. If you want to make Text or Listbox widgets
mouse-wheel-aware, you can use the method below (borrowed from the
Tcl/Tk library), e.g. $text->BindMouseWheel. Note that I changed the
scrolling delta from the original 4 or 5 lines to 3 (which seems to
match the behaviour on my NT machine).

# not yet tested on Unix
sub Tk::Widget::BindMouseWheel {
    my($w) = @_;

    # The MouseWheel will typically only fire on Windows.  However,
    # someone could use the "event generate" command to produce one
    # on other platforms.

    $w->bind('<MouseWheel>',
              [ sub { $_[0]->yview('scroll',-($_[1]/120)*3,'units') }, Tk::Ev("D")]);

    if ($Tk::platform eq 'unix') {
        # Support for mousewheels on Linux/Unix commonly comes through mapping
        # the wheel to the extended buttons.  If you have a mousewheel, find
        # Linux configuration info at:
        #   http://www.inria.fr/koala/colas/mouse-wheel-scroll/
        $w->bind('<4>',
                 sub { $_[0]->yview('scroll', -3, 'units')
                           unless $Tk::strictMotif;
                   });
        $w->bind('<5>',
                 sub { $_[0]->yview('scroll', 3, 'units')
                           unless $Tk::strictMotif;
                   });
    }
}