//preload the images

var nav1_on  = new Image();
nav1_on.src  = "images/nav/1-on.gif";
var nav1_off = new Image();
nav1_off.src = "images/nav/1-off.gif";

var nav2_on  = new Image();
nav2_on.src  = "images/nav/2-on.gif";
var nav2_off = new Image();
nav2_off.src = "images/nav/2-off.gif";

var nav3_on  = new Image();
nav3_on.src  = "images/nav/3-on.gif";
var nav3_off = new Image();
nav3_off.src = "images/nav/3-off.gif";

var nav4_on  = new Image();
nav4_on.src  = "images/nav/4-on.gif";
var nav4_off = new Image();
nav4_off.src = "images/nav/4-off.gif";

var nav5_on  = new Image();
nav5_on.src  = "images/nav/5-on.gif";
var nav5_off = new Image();
nav5_off.src = "images/nav/5-off.gif";

var nav6_on  = new Image();
nav6_on.src  = "images/nav/6-on.gif";
var nav6_off = new Image();
nav6_off.src = "images/nav/6-off.gif";

function swap_image_on(id) {
	if(eval(id + '_on.complete')) {
		document.getElementById(id).src = eval(id + '_on.src');
	}	
}

function swap_image_off(id) {
	if(eval(id + '_off.complete')) {
		document.getElementById(id).src = eval(id + '_off.src');
	}		
}