function centerItem(item){
	var offset = (jQuery(window).width() - item.width())/2;
	item.css("left",offset+"px");
}
$(document).ready(function(){
	centerItem(jQuery("#mainBackground"));
	centerItem(jQuery("#footer"));
	jQuery(window).resize(function(){
		centerItem(jQuery("#mainBackground"));
		centerItem(jQuery("#footer"));	
	});
});