GridView1.DataSource=MyDataTable

<asp:TemplateField HeaderText="[-]">
   <ItemTemplate>
      <asp:CheckBox runat="server"/>
   </ItemTemplate>
</asp:TemplateField>

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As _
  System.EventArgs) Handles Button1.Click
   For Each MyRowX As GridViewRow In GridView1.Rows
      '... ich hab keine Ahnung
   Next
End Sub