prova così;
...
<style>
<!--
html{height:100%;}
body{height:100%;}
#tbl{height:100%;}
#rowtop{height: xxpx;}
#rowbot{height: xxpx;}
-->
</style>
...
<body>
<table>
<tr id="rowtop">
<td></td>
</tr>
<tr><td></td></tr>
<tr id="rowbot">
<td></td>
</tr>
</table>
...