C#

public static bool Report(int hwnd, int lParam) { 
      Console.Write("Window handle is ");
      Console.WriteLine(hwnd);
      return true;
   }

/**** NativeMethods.cs ***/
public class NativeMethods
{
 public NativeMethods(){}
 [StructLayout(LayoutKind.Sequential)]
 public struct CopyDataStruct
 {
 public string ID;
 public int Length;
 public string Data;
 }
 [DllImport("user32.dll", EntryPoint="FindWindow")]
 public extern static System.IntPtr FindWindow(string lpClasName,
                                    string lpWindowName);
 public const int WM_COPYDATA = 0x004a;
 [DllImport("user32.dll", EntryPoint="SendMessage")]
 public extern static int SendMessage(System.IntPtr hWnd,
                          int Msg, int wParam,
                          ref CopyDataStruct lParam);
}

/**** SendingForm.cs ***/
private void SendingForm_Load(object sender, System.EventArgs e)
{
 ReceivingForm rec = new ReceivingForm();
 rec.Show();
}

private void button1_Click(object sender, System.EventArgs e)
{
 NativeMethods.CopyDataStruct DataStruct = new NativeMethods.CopyDataStruct
();
 DataStruct.ID = "1";
 DataStruct.Data = "Sample Text";
 DataStruct.Length = DataStruct.Data.Length;
 IntPtr WHnd = NativeMethods.FindWindow(null, "ReceivingForm");
 if(!WHnd.Equals(System.IntPtr.Zero))
 {
  NativeMethods.SendMessage(WHnd, NativeMethods.WM_COPYDATA,
                            0, ref DataStruct);
 }
}

/**** ReceivingForm.cs ***/
protected override void WndProc(ref Message m)
{
 switch(m.Msg)
 {
 case(NativeMethods.WM_COPYDATA) :
  NativeMethods.CopyDataStruct ds =
(NativeMethods.CopyDataStruct)m.GetLParam(typeof
(NativeMethods.CopyDataStruct));
  string s = ds.Data;
  break;
 default :
  break;
 }
 base.WndProc(ref m);
}

Stupidity dies.
The end of future offspring.
Evolution wins.
- A Darwin Awards Haiku