function changetab(td, links, out1, out2, out3) {
    td.style.backgroundImage='url(media/misc/tab_bt_yellow_over.gif)';
    document.getElementById(links).style.visibility='visible';
    document.getElementById(out1).style.visibility='hidden';
    document.getElementById(out2).style.visibility='hidden';
    document.getElementById(out3).style.visibility='hidden';
}
function changetab2(td) {
    td.style.backgroundImage='url(media/misc/tab_bt_yellow.gif)';
}

function changetab3 (td, links, out1, out2, out3) {
    td.style.backgroundImage='url(media/misc/tab_bt_blue_over.gif)'
    document.getElementById(links).style.visibility='visible';
    document.getElementById(out1).style.visibility='hidden';
    document.getElementById(out2).style.visibility='hidden';
    document.getElementById(out3).style.visibility='hidden';
}

function changetab4 (td) {
    td.style.backgroundImage='url(media/misc/tab_bt_blue.gif)'
}

function changetab_all () {
    document.getElementById('subnav1').style.visibility='hidden';
    document.getElementById('subnav2').style.visibility='hidden';
    document.getElementById('subnav3').style.visibility='hidden';
    document.getElementById('subnav4').style.visibility='hidden';
}