最简单的办法:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim frm As New Form2
frm.Owner = Me
frm.Show()
Me.Hide()
End Sub
在FORM2中
Private Sub Form2_Closed(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Closed
Dim frm As Form = Me.Owner
frm.Close()
End Sub