/* 
 * == jQuery ==
 */

$(function() {

    //$('.img_list_nonjs').removeClass().addClass('img_list_js');

   $('.thumb_link').click(function(){
        var img = $($(this).attr('href'));
        //or however you get a handle to the IMG
        var width = img.clientWidth;
        var height = img.clientHeight;

        $('.main_img').attr('src', $(this).attr('href'));

        if(width < 600 && width > 400 && width > height)
            $('.main_img').css('width', '600px');
        
        return false;
    });

});