Stupid beginner question :o)

Hi there, I'm just starting to work with C# and the ADO.NET. As a test project i've choosen a simple Customer-Management Application. So here's my problem: In my main form I have a DataGrid that should display all my Customers. I have a MainMenu and there I select "Add new Customer", wich opens a form to enter the Data and saves it in a DataSet (and in an XML-File). How do I update the DataGrid in the Main Window, when a Customers has been enterd in my "frmAddCustomer" form? I now create the Dataset for storing the Customer-Data in the btnSave_Click Method. Do I have to use the DataSet from the MainWindow...and if so HOW? :o) Please help a newbie. :o) Kind regards, Iceman