do you want to split the screen in equal parts, or like the home page of codenewbie? you can always use table padding
something like this would fill the entire screen:
PHP Code:
<table border=0 cellspacing=0 cellpadding=20 width=100% height=100%>
<tr>
<td width=150 valign=top> left cell </td>
<td valign=top> no width here, it will stretch </td>
<td width=150 valign=top> right cell </td>
</tr>
</table>
hope this helps.