function rollover(pagename) {
    document.getElementById(pagename+'-nav').src = '/images/nav/'+pagename+'_on.png';
    document.getElementById(pagename+'-nav').style.backgroundImage = 'url(/images/nav/nav_on.png)';
}

function rollout(pagename) {
    document.getElementById(pagename+'-nav').src = '/images/nav/'+pagename+'_off.png';
    document.getElementById(pagename+'-nav').style.backgroundImage = 'url(/images/nav/nav_off.png)';
}