'En un form, agregar:
'    2 textos: txtUser y txtSerial
'    1 boton:Command1

Private Sub Command1_Click()
Dim a As String
Dim i As Integer

txtSerial.Text = ""
For i = 1 To Len(txtUser.Text)
    txtSerial.Text = txtSerial.Text + Chr(Asc(Mid(txtUser.Text, i, 1)) + 5)
Next i
End Sub