This is a major difference between vb6 and .NET. In .NET, forms are truly classes, as opposed to the pseudo-classes that they were in vb6. As such, when you create a frmMain with the frmDesigner, you have created a class called frmMain. Thusly, you must create a new instance of it, A la this:
VB Code:
  1. Dim myForm as New frmMain

  2. myForm.Show

Good luck!