Give this a try:
<body>
<table width="100%" height="100%" border="1">
<tr>
<td height="250"> </td>
</tr>
<tr>
<td><iframe name="content" frameborder="0" src="src.htm" height="100%" width="100%" scrolling="auto" marginheight="0" marginwidth="0"></iframe></td>
</tr>
<tr>
<td height="100"> </td>
</tr>
</table>
</body>