formato en un textbox en vb6 o visual basic 6

[vdiaz18]

saludos, podrias hacerlo de la siguiente manera:

Private Sub Text1_LostFocus()
Dim A(13), B(13) As String
For i = 1 To 12
A(i) = Mid(Text1.Text, i, 1)
Next
B(5) = "-"
For i = 1 To 4
B(i) = A(i)
Next
For i = 6 To 13
B(i) = A(i)
Next
For i = 1 To 13
texto = texto + B(i)
Next
Text1 = texto
End Sub

Espero te sirva