strict VS transitional??

What are the differens between these 2 lines?

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 strict//EN" >
VS
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 transitional//EN" >

What does strict do that transitional doesnt??

This code works when I hav strict but not when I have transitional, why??

VB Code:

<table height='150px' width='150px' border='1'>
  <tr>
    <td>Pelle
<span id="BilockListView1" style="height:100px;width:100px;">
<div style='height:100px;width:100px'>
<div style='overflow: scroll;overflow-x:hidden;height:100%' id='tC'>
<table ID='BilockListView1'>
<tr style="top:expression(document.getElementById('tC').scrollTop);position:relative;">
<td>PubId</td>
<td>OrgName</td>
<td>Edition</td>
</tr>
 
<tr><td>4</td><td>654 SMO Datasheet</td><td>-99</td></tr>
<tr><td>1</td><td>AvestaPolarit Stainless Steel</td><td>-00</td></tr>
<tr><td>3</td><td>Machining handbook</td><td>-99</td></tr>
<tr><td>2</td><td>Welding guidelines</td><td>-99</td></tr>
 
</table></div></div></span>
    </td>
    <td>Olle</td>
   </tr>
</table>