...
<Script Language="JavaScript">
  <!--
      function CountItem() {
         var Count=0;
         for(i=0;i<TheSelect.length;i++)
            if(TheSelect.options[i].selected==true)
                 Count++;
         alert("共有["+Count+"]项被选中!!!");
      }
  -->
</Script>
<Body>
<Select Name="TheSelect" Multiple>
  <Option>China</Option>
  <Option>Japan</Option>
  <Option>Korea</Option>
  <Option>U.S.A</Option>
</Select>
<Input Type=Button Value="统计" OnClick="CountItem()">
</Body>
</Html>