La forma mas sencilla seria
  
Código:
 Private Sub Text2_KeyPress(KeyAscii As Integer) 'Seria el text de contraseña
If KeyAscii = 13 Then
    If Text1.Text = "Administrador" And Text2.Text = "TPHMM23VQK" Then
       Form2.Show
       Unload Me
   Else
      MsgBox "DATOS INCORRECTOS"
   End If
End If
End Sub
  
Otra forma de hacerlo es utilizando una funcion:   
Código:
 Private Function autentificar(user As String, pass As String)
If user = "Administrador" And pass = "TPHMM23VQK" Then
   Form2.Show
   Unload Me
Else
   MsgBox "DATOS INCORRECTOS"
End If
End Function
Private Sub Text2_Keypress(KeyAscii As Integer)
If KeyAscii = 13 Then a = autentificar(Text1.Text, Text2.Text)
End Sub