Class_getElementPosition = function(elemId){
    var elem = document.getElementById(elemId);
    var w = elem.offsetWidth;
    var h = elem.offsetHeight;
    var l = 0;
    var t = 0;
    while (elem){
        l += elem.offsetLeft;
        t += elem.offsetTop;
        elem = elem.offsetParent;
    }
    return {"left":l, "top":t, "width": w, "height":h};
}

function position_footer(id_footer_bottom, id_content){
	document.getElementById(id_content).style.height = 'auto';
	document.getElementById(id_footer_bottom).style.top = '0px';
	var obj_getElementPosition_footer = new Class_getElementPosition(id_footer_bottom);
	var obj_getElementPosition_content = new Class_getElementPosition(id_content);
	var h_body = (document.compatMode=='CSS1Compat' && !window.opera?document.documentElement.clientHeight:document.body.clientHeight);
	if(h_body > obj_getElementPosition_footer.top + obj_getElementPosition_footer.height){
		document.getElementById(id_content).style.height = obj_getElementPosition_content.height + h_body - obj_getElementPosition_footer.top - obj_getElementPosition_footer.height + 'px';
	}
}
function start_run(id_footer_bottom, id_content){
	position_footer(id_footer_bottom, id_content);
	setInterval("position_footer('"+id_footer_bottom+"','"+id_content+"')", 500);
}
//start_run('bg_footer', 'content');