show hide Javascript not working in IE 6 , Safari

Question

Dear Friends,

The following code is working fine in Mozilla firefox, opera. But not working in IE6  and safari.. Pls help me guys
THANKS IN ADVANCE>>>>>>>>>>>>>>

<select name="dsrtype">
                                                    <option value="0">-Select-</option>
                                                    <option value="a" onclick="document.getElementById('LWE_show').style.display='';document.getElementById('hidden').style.display='none';">Op1</option>
                                                    <option value="b" onclick="document.getElementById('hidden').style.display='';document.getElementById('LWE_show').style.display='none';">Opt2</option>
</select>