Can't update database with SQL dataAdapter

Hi,
Being new to database programming, I am trying my hand at using code (as opposed to dragging the graphical componants to the form).

I have a simple database on SQL server 2005 express, connected to a Windows form. When trying to update changes I make to to the fields on the form using the sqldataAdapter update command the changes are not committed to the databse.
I use the following line of code to perform the update:

DataAdapterCustomers.Update(DataSetCustomers)

The connection, dataAdapter and dataset were created using the following code:
-------------------------
        Dim sConnectionString As String = _
             "data source=TONI\SQLEXPRESS;" & "initial catalog=Murach;integrated security=SSPI;" & _
             "persist security info=false;workstation id=TONI;packet size=4096"
        Dim cnn As New SqlConnection(sConnectionString)
     The Select statement
    Dim sCustomersSelect = "Select * from Customers"
    Dim DataAdapterCustomers As New SqlDataAdapter(sCustomersSelect, cnn)
       Dim DataSetCustomers As New DataSet()  
---------------
I think I need to configure my dataAdapter, but I have no idea how to do that in code. Please help.