<tr>
        <td>
          <select size="5" id='id1' onChange="show_list(getElementById('id1').value)">
           <option value='1'> 1 </option>
           <option value='2'> 2 </option>
           <option value='3'> 3 </option>
           <option value='4'> 4 </option>
          </select>
     </td>
		
     <td align='center' id='show'>
     </td>
</tr>

        <select>
           <option value='1'>Иван</option>
           <option value='2'>Василий</option>
          </select>

        <select>
           <option value='1'>Петр</option>
           <option value='2'>Генадий</option>
          </select>

function show_list(selected) 
  {
     if (selected== 1 )
      {
          $("show").html('<select>'+
           '<option value=' 1 '>Иван</option>'+
           '<option value=' 2 '>Василий</option>'+
           '</select>')
       }
     else
      if (selected== 2 )
       {
        .............
       }
   }