There is a great article on CodeProject, by Guenter Prossliner.

A simple class in presented there, that makes Duck Typing possible for Generics enabled CLS languages (VB.NET 8 and C#2.0 for instance).

I'll present it here in short form:

let's say we have two classes:

   1:  class Foo1
   2:  {
   3:      public string Bar() { }
   4:  }
   5:  class Foo2
   6:  {
   7:      public string Bar() { }
   8:  }

Now you have a method that can work with instances of eiether one, and invoke Bar on it:

   1:  void SimpleMethodOnFoo1(Foo1 foo)
   2:  {
   3:      foo.Bar();
   4:  }
   5:  void SimpleMethodOnFoo2(Foo2 foo)
   6:  {
   7:      foo.Bar();
   8:  }