function windowOnload(f) {
    var prev=window.onload;
    window.onload=function(){ if(prev)prev(); f(); }
}

function changeProperty(id,property,value){
	var object = document.getElementById(id);
	object[property] = value;
}

function headLinks (){

	var header = document.getElementById('header');

	header.onmouseover = function(){ header.src = 'img/about_us_header_yellow.png'; }
	header.onmouseout = function(){ header.src = 'img/about_us_header_blue.png'; }
	
	var mail = document.getElementById('mail');

	mail.onmouseover = function(){ mail.src = 'img/mail_yellow.png'; }
	mail.onmouseout = function(){ mail.src = 'img/mail_blue.png'; }
}

windowOnload( headLinks );