body {
background: url('bg.jpg') no-repeat top center;
margin: 0 0 0 0;
font-family: Tahoma, Verdana, Arial;

<SCRIPT LANGUAGE="JavaScript">
if (screen.width == '1600')
{location.href='1600.htm'}

if (screen.width == '1280')
{location.href='1280.htm'}

if (screen.width == '1152')
{location.href='1042.htm'}

if (screen.width == '1024')
{location.href='1024.htm'}

if (screen.width == '800')
{location.href='800.htm'}

if (screen.width == '640')
{location.href='640.htm'}

if (screen.width <= '639')
{location.href='640.htm'}
</SCRIPT>
}