$(document).ready(function() { centerContent(); });	
$(window).resize(function() { centerContent(); });

function centerContent() {
	var winW=$(window).width();
	var winH=$(window).height();
	
	if (winH>480) {
		var mainTmargin = (winH-480)/2;
		$("#main").css("margin-top", mainTmargin + "px");
	}
	else {
		$("#main").css("margin-top", "0px");
	}
	
	if (winW>920) {
		var mainLmargin = (winW-920)/2;
		$("#main").css("margin-left", mainLmargin + "px");
	}
	else {
		$("#main").css("margin-left", "0px");
	}
}