$(function() {
    var $current = $("#container li"),
        len = $current.length-1,
        current = 0;
    
    $("#next, #prev").click( function(){
        current += (this.id === 'next') ? 1 : -1;
        if (current < 0) {
            current = 0;
            return;
        }
        if (current > len) {
            current = len;
            return;
        }
        $current.animate({
            left: -790*current,
            top: 0 
        });
    });
});​