function roll_in(imgsrc, myID){
    document['top_image'].src = imgsrc;
    document.getElementById(myID).style.backgroundColor = '#ffffff';
    document.getElementById(myID).style.color = '#000000';
}

function roll_out(myID){
    document['top_image'].src = 'http://www.hydrosight.com/images/_index/underwater_windows_overview.jpg';
    document.getElementById(myID).style.backgroundColor = '';
    document.getElementById(myID).style.color = '#ffffff';
}

if (document.images) {

    img1 = new Image();
    img1.src = "http://www.hydrosight.com/images/_index/2mermaids.jpg";
    img2 = new Image();
    img2.src = "http://www.hydrosight.com/images/_index/jana-04.jpg";
    img3 = new Image();
    img3.src = "http://www.hydrosight.com/images/_index/dicker_block.jpg";
    img4 = new Image();
    img4.src = "http://www.hydrosight.com/images/_index/dream_on_yacht.jpg";
    img5 = new Image();
    img5.src = "http://www.hydrosight.com/images/_index/tunnel_seal.jpg";
    img6 = new Image();
    img6.src = "http://www.hydrosight.com/images/_index/underwater_windows_overview.jpg";
}