<table id="myT" width="100%"  height="100%" border="0" cellspacing="0" cellpadding="0">
 <tr>
   <td>test</td>
 </tr>
</table>

alert(document.all["myT"].offsetWidth+" : "+document.all["myT"].offsetHeight);
alert(document.all["myT"].clientWidth+" : "+document.all["myT"].clientHeight);

alert(document.getElementById("myT").offsetWidth+" : "+document.getElementById("myT").offsetHeight);
alert(document.getElementById("myT").clientWidth+" : "+document.getElementById("myT").clientHeight);