一段小小的js代码

<div>
<select id="oSelect1" name="Cars" size="10" multiple="multiple">
<option value="1">BMW</option>
<option value="2">Porsche</option>
<option value="3" >Mercedes</option>
</select>
<input type="button" onclick="choose('oSelect1', 'oSelect2')" value=">>" />&nbsp;
<input type="button" onclick="choose('oSelect2', 'oSelect1')" value="<<" />
<select id="oSelect2" name="Cars" multiple="multiple" style="width: 95px; height: 160px">
</select><br />
    &nbsp;
</div>
</body>
</html>
<script language="javascript" type="text/javascript"> 
    function choose(src, dst)
    {
        var oSelect1 = document.getElementById(src);
        var oSelect2 = document.getElementById(dst);
       
        var opts = new Array();          
        var i;                   
        
        for(i = 0; i < oSelect1.options.length; i++)
        {           
            var item = oSelect1.options[i];       
            if(item.selected)
            {
               opts.push(item);               
             }
        }      
       
        for(i = 0; i < opts.length; i++)
        {           
            var opt = document.createElement("<option>");
            opt.text = opts[i].text;
            opt.value = opts[i].value;
           
            if(navigator.appName == 'Microsoft Internet Explorer') {
                oSelect2.add(opt);
                //oSelect2.add(opt, null); // IE 不支持
                //oSelect2.appendChild(opt); // IE 不支持,可以添加，但是不显示，^||^
            }
            else {
                //oSelect2.add(opt);      // firefox 不支持
                oSelect2.add(opt, null);               
                //oSelect2.appendChild(opt); // firefox 支持
            }
           
            oSelect1.removeChild(opts[i]);                   
        }
    }