Hi,
you can easy achieve this with the normal combo like that:
	<select id="cc2" style="width:150px"></select>
    <div id="sp">
        <div style="color:#99BBE8;background:#fafafa;padding:5px;">Select a language</div>
        <input type="checkbox" name="lang" value="01"><span>Java</span><br/>
        <input type="checkbox" name="lang" value="02"><span>C#</span><br/>
        <input type="checkbox" name="lang" value="03"><span>Ruby</span><br/>
        <input type="checkbox" name="lang" value="04"><span>Basic</span><br/>
        <input type="checkbox" name="lang" value="05"><span>Fortran</span>
    </div>
            $('#cc2').combo({
                required:true,
                editable:false,
		multiple:true
            });
           $('#sp').appendTo($('#cc2').combo('panel'));
           $('#sp input').click(function(){
				var my_text = '';
				var my_val = '';
		   
				$('#sp input').each(function(){
					if ($(this).is(":checked")) {
						var v = $(this).val();
						var s = $(this).next('span').text();
						
						my_text == '' ? my_text = s : my_text += ','+s;
						my_val  == '' ? my_val = v : my_val += ','+v;	
					}
				});
				$('#cc2').combo('setValue', my_val).combo('setText', my_text);
            });