You need to retain a reference to the form somewhere, so that you can
reuse the original form instance.  There are a variety of ways to do
this, but making the form a singleton may be the cleanest technique for you:

    public class Form1 : Form
    {
        static Form1 _instance;

        public static Form1 Instance
        {
            get
            {
                if (_instance == null)
                {
                    _instance = new Form1();
                }

                return _instance;
            }
        }

        private Form1()
        {
            InitializeComponent();
            /* other initialization, etc. */
        }
    }

You will need to change your Program class so that it uses
"Form1.Instance" rather than "new Form1()" in the Application.Run()
statement.  (See a recent thread for alternatives to this:
http://groups.google.com/group/microsoft.public.dotnet.languages.csharp/browse_t
hread/thread/9e92d24414f6bfe5/)

Then, elsewhere when you want the instance, you also use
"Form1.Instance" instead of constructing a new one yourself.

Pete