function toggleNav(id, type) {  
    obj = document.getElementById(id);
    images = new Array;
    switch(type) {
      case 'arrows':     
        images['open'] = 'url(http://library.buffalo.edu/libraries/img/icon_bluearrow_down.gif)';
        images['closed'] = 'url(http://library.buffalo.edu/libraries/img/icon_bluearrow.gif)';
        break;
      case 'plus-minus':
        images['open'] = 'url(http://library.buffalo.edu/libraries/img/icon_bluearrow_down.gif)';
        images['closed'] = 'url(http://http://library.buffalo.edu/libraries/img/icon_bluearrow.gif)';
        break;
    }  
    if (obj.style.backgroundImage == images['closed']) {
      obj.style.backgroundImage = images['open']
    } else {
      obj.style.backgroundImage = images['closed']
    }
}