For Each form As Form In My.Application.OpenForms
If form Is My.Forms.FormYouCheck Then
'do something (it's open)
End If
Next
Public Function IsFormOpen(ByVal FormName As String) As Boolean
Dim frm As Form
IsFormOpen = False
For Each frm In My.Application.OpenForms
If frm.Name = FormName Then
IsFormOpen = True
Exit For
End If
Next
End Function