function newImage(arg) {
	if (document.images) {
		rslt = new Image();
		rslt.src = arg;
		return rslt;
	}
}

function changeImages() {
	if (document.images && (preloadFlag == true)) {
		for (var i=0; i<changeImages.arguments.length; i+=2) {
			document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
		}
	}
}

var preloadFlag = false;
function preloadImages() {
	if (document.images) {
		nav_home_over = newImage("images/nav/nav-home-over.jpg");
		nav_about_over = newImage("images/nav/nav-about-over.jpg");
		nav_products_over = newImage("images/nav/nav-products-over.jpg");
		nav_gallery_over = newImage("images/nav/nav-gallery-over.jpg");
		nav_warranty_over = newImage("images/nav/nav-warranty-over.jpg");
		nav_contact_over = newImage("images/nav/nav-contact-over.jpg");
		preloadFlag = true;
	}
}


function open_popup(url, winName, winWidth, winHeight){
		window.open(url,winName,'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=0,resizable=0,left='+centre(winWidth,screen.availWidth)+',top='+centre(winHeight,screen.availHeight)+',width='+winWidth+',height='+winHeight);
}
		
function centre(size,area){return (area/2)-(size/2);
}