How to comment a method in Visual Studio 2008/2010

You use XML Documentation with 3 slashes (///)

   /// <summary>
   /// Description for SomeMethod.</summary>
   /// <param name="s"> Parameter description for s goes here</param>
   /// <seealso cref="String">
   /// You can use the cref attribute on any tag to reference a type or member 
   /// and the compiler will check that the reference exists. </seealso>
   public void SomeMethod(string s)
   {
   }

Here you can find a tutorial on this type of documentation with a lot of examples.