if(document.images)
{
    nav = new Array();
    nav[01] = new Image();
    nav[01].src = "images/btn_intro.gif";
    nav[02] = new Image();
    nav[02].src = "images/btn_intro_ovr.gif";
    nav[03] = new Image();
    nav[03].src = "images/btn_contact.gif";
    nav[04] = new Image();
    nav[04].src = "images/btn_contact_ovr.gif";
}


function change_nav(from,to)
{
    if(document.images)
    {
        document.images[from].src = nav[to].src;
    }
}