static StartUpHandler myStartUpHandler;
        static Form1 mySingleForm1;
        [STAThread]
        public static void Main(string[] CmdArgs)
        {
            myStartUpHandler = new StartUpHandler();
            myStartUpHandler.CallbackEvent += new _
              StartUpHandler.CallbackEventHandler( _
              m_objStartuphandler_CallbackEvent);
            myStartUpHandler.Host = "127.0.0.1";
            myStartUpHandler.Port = 57349;
            myStartUpHandler.UniqueMutexId = "MYSUPER_UNIQUE_ID";
            myStartUpHandler.Run(CmdArgs);
        }
 
        private static void m_objStartuphandler_CallbackEvent(object sender, _
          StartUpEventArgs e)
        {
            FormSplash m_frmSplash;
            m_frmSplash = new FormSplash();
            m_frmSplash.ShowDialog(1000);
            if (e.IsFirst)
            {
                mySingleForm1 = new Form1();
                if (e.CmdArgs.Length > 0)
                {
                }
                else
                {
                    mySingleForm1.ShowDialog();
                }
                mySingleForm1 = null;
            }
            else
            {
                if (e.CmdArgs.Length > 0)
                {
                }
                if (mySingleForm1.WindowState == FormWindowState.Minimized)
                {
                    mySingleForm1.WindowState = FormWindowState.Normal;
                }
                mySingleForm1.TopMost = true;
                mySingleForm1.BringToFront();
            }
        }
 
        public class StartUpHandler : MarshalByRefObject
        {
            System.Threading.Mutex m_objMutex;
            System.Runtime.Remoting.Channels.Tcp.TcpChannel m_objChannel;
            string m_strId;
            string m_strHost;
            int m_intPort;
            public event CallbackEventHandler CallbackEvent;
            public delegate void CallbackEventHandler(object sender, _
              StartUpEventArgs e);
 
            public void Run(string[] args)
            {
                bool createdNew = true;
                m_objMutex = new System.Threading.Mutex(false, m_strId, out _
                  createdNew);
                if (m_objMutex.WaitOne(1, true))
                {
                    CreateInstanceChannel();
                    StartUpEventArgs event_args = new StartUpEventArgs(true, _
                      args);
                    DoCallback(event_args);
                }
                else
                {
                    StartUpEventArgs event_args = new StartUpEventArgs(false, _
                      args);
                    UseInstanceChannel(event_args);
                }
            }
 
            //Properties
 
            private void CreateInstanceChannel()
            {
                IDictionary m_objTcpConfig = new Hashtable(2);
                System.Runtime.Remoting.RemotingServices.Marshal(this, m_strId);
                m_objTcpConfig["bindTo"] = m_strHost;
                m_objTcpConfig["port"] = m_intPort;
                m_objChannel = new _
                  System.Runtime.Remoting.Channels.Tcp.TcpChannel( _
                  m_objTcpConfig, null, null);
                System.Runtime.Remoting.Channels.ChannelServices.RegisterChanne_
                l(m_objChannel, true);
            }
 
            private void UseInstanceChannel(StartUpEventArgs event_args)
            {
                try
                {
                    string m_strAddress = "tcp://" + m_strHost + ":" + _
                      m_intPort + "/" + m_strId;
                    StartUpHandler m_objRemoteHandler = new StartUpHandler();
                    m_objRemoteHandler = ( _
                      StartUpHandler)System.Runtime.Remoting.RemotingServices.C_
                      onnect(typeof(StartUpHandler), m_strAddress);
                    m_objRemoteHandler.DoCallback(event_args);
 
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
 
            public void DoCallback(StartUpEventArgs event_args)
            {
                MessageBox.Show("doo callback");
                CallbackEvent(this, event_args);
            }
        }

fg viperbone