// Hide all but the first
$('.selectoption li').not(':first').hide();

// Handle the click of prev and next links
$('.prev,.next').click(function() {
    // Determine the direction,-1 is prev,1 is next
    var dir = $(this).hasClass('prev') ? -1 : 1;
    // Get the li that is currently visible
    var current = $('.selectoption li:visible');

    // Get the element that should be shown next according to direction
    var new_el = dir < 0 ? current.prev('li') : current.next('li');

    // If we've reached the end,select first/last depending on direction
    if(new_el.size() == 0) {
        new_el = $('.selectoption li:'+(dir < 0 ? 'last' : 'first'));
    }

    // Hide them all..
    $('.selectoption li').hide();
    // And show the new one
    new_el.show();

    // Prevent the link from actually redirecting the browser somewhere
    return false;
});