gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Intranet
{
    public static class MenuExtensions
    {
        public static IMenu NextSibling(this IMenu menu)
        {
            if (menu.Parent == null)
                throw new InvalidOperationException("I'm the root menu node, I have no parents!");
            return (from n in menu.Parent.Nodes
                    where n.Order >= menu.Order
                    orderby n.Order
                    select n).FirstOrDefault();
        }

        public static IMenu NextParent(this IMenu menu)
        {
            return menu.Parent.NextSibling();
        }
    }
}