Hola!!!
 
En el Deposito de JS vienen un par de ejemplos de lo ke buscas. 
Ahi van: 
<!-- Detectar y redireccionar segun resolución de pantalla --> 
<script LANGUAGE="JavaScript"> 
function redireccionar() {
var url640x480 = "http://www.tu-sitio.com/640x480";
var url800x600 = "http://www.tu-sitio.com/800x600";
var url1024x768 = "http://www.tu-sitio.com/1024x768";
if ((screen.width == 640) && (screen.height == 480)) 
window.location.href= url640x480;
else if ((screen.width == 800) && (screen.height == 600))
window.location.href= url800x600;
else if ((screen.width == 1024) && (screen.height == 768))
window.location.href= url1024x768;
else window.location.href= url640x480;
} 
</script> 
<!-- Maximizar ventana --> 
<script language="JavaScript">
<!-- 
// Maximizar Ventana por Nick Lowe (
[email protected]) 
window.moveTo(0,0);
if (document.all) {
top.window.resizeTo(screen.availWidth,screen.avail  Height);
}
else if (document.layers||document.getElementById) {
if (top.window.outerHeight<screen.availHeight||top  .window.outerWidth<screen.availWidth){
top.window.outerHeight = screen.availHeight;
top.window.outerWidth = screen.availWidth;
}
}
//-->
</script> 
Espero te sirvan!!! 
Bye ;)