Master Page Fix Height

<form id="form2" runat="server">

<div>

<table border="0" width="100%">

<tr>

<td colspan="2" height="150" bgcolor="gray" valign="middle"  align="center">

HEADER

</td>

</tr>

<tr>

<td width="20%" bgcolor="silver">SIDEBAR</td>

<td width="80%" height="400" bgcolor="white">

<asp:contentplaceholder id="ContentPlaceHolder1" runat="server">

</asp:contentplaceholder>

</td>

</tr>

<tr>

<td colspan="2" align="center" height="20" bgcolor="gray">

FOOTER

</td>

</tr>

</table>

</div>

</form>