function highlightNavButton(buttonId) 
{
    document.getElementById(buttonId).src = "img/" + buttonId + "_on.gif";
}

function unhighlightNavButton(buttonId) 
{
    document.getElementById(buttonId).src = "img/" + buttonId + ".gif";
}

//Preload images for better performance
if (document.images) 
{
    //bio images
    var img1 = new Image();
    var img2 = new Image();
    var img3 = new Image();
    var img4 = new Image();
    var img5 = new Image();
    var img6 = new Image();
    var img7 = new Image();

    img1.src = "img/bio_dale.jpg";
    img2.src = "img/bio_erin.jpg";
    img3.src = "img/bio_greg.jpg";
    img4.src = "img/bio_johnny.jpg";
    img5.src = "img/bio_kenny.jpg";
    img6.src = "img/bio_mike.jpg";
    img7.src = "img/bio_russ.jpg";

    //button images
    var img10 = new Image();
    var img11 = new Image();
    var img12 = new Image();
    var img13 = new Image();
    var img14 = new Image();
    var img15 = new Image();
    var img16 = new Image();
    var img17 = new Image();
    var img18 = new Image();
    var img19 = new Image();
    var img20 = new Image();
    var img21 = new Image();
    var img22 = new Image();
    var img23 = new Image();
    var img24 = new Image();
    var img25 = new Image();

    img10.src = "img/button_bios.gif";
    img11.src = "img/button_bios_on.gif";
    img12.src = "img/button_booking.gif";
    img13.src = "img/button_booking_on.gif";
    img14.src = "img/button_calendar.gif";
    img15.src = "img/button_calendar_on.gif";
    img16.src = "img/button_home.gif";
    img17.src = "img/button_home_on.gif";
    img18.src = "img/button_links.gif";
    img19.src = "img/button_links_on.gif";
    img20.src = "img/button_music.gif";
    img21.src = "img/button_music_on.gif";
    img22.src = "img/button_photos.gif";
    img23.src = "img/button_photos_on.gif";
    img24.src = "img/button_videos.gif";
    img25.src = "img/button_videos_on.gif";
}