I have written a short script that checks if a user has a screen rez lower than 1025 (so that the ipad is included) if it is bigger than 1025 then it centres a div according to the screen size.

<script type="text/javascript">
if ((screen.width<=1025)) {
alert("Mobile device!");
}
else{
document.getElementById('page').style.left = (((screen.width-1000)/2)+'px');
}
</script>

change 1000 to your screen size
and add a div with the ID:'page'