function isDefined(id){
		if($(id) == null){
			if(document.getElementsByName(id).length == 0)
				return false;
		}else{
			return true;
		}
	}

	function fadeIn(id){
		if(isDefined(id)){
			new Effect.Appear(id);
		}
	}

	function fadeOut(id){
		if(isDefined(id)){
			new Effect.Fade(id);
		}
	}

	function validateZip(e){
		var is_valid	=	/^\d{5}$/.test($F("zip"));
		
		if(!is_valid){
			fadeIn("zip_error");
			Event.stop(e);
		}else{
			fadeOut("zip_error");
		}
	}

	function validateOnReturnKey(e){
		if(e.keyCode == Event.KEY_RETURN){
			validateZip(e);
		}
	}

	if (	!(BrowserDetect.browser == "Explorer" && BrowserDetect.version < 6)	) {
		Event.observe(	window, "load", function() {
			Event.observe(document, "keypress", function(e){ validateOnReturnKey(e); });
			Event.observe("submit", "click", function(e){ validateZip(e); });
		});
	}