[jQuery] next() and prev()

[PaulC]

I'm stuck using next() and prev()

The menu on right hand side of this site: http://sugarsnap.previewurl.net
needs to scroll through each item as the user clicks the arrows. This
is working but only because I've put fixed heights to scroll -
which is buggy cross browser., hence wanting to use next() and prev()

the code that works:

$('a.down').click(function(event) {
      $('#folioMenu').scrollTo('+=90px', 800);
      return false;
});

I tried this , and several variations, wiht no luck:

$('#folioMenu').scrollTo($(".menuItem").next(), 800);

any thoughts as to how this could be achieved?