If txtPasswort.Text.Length >= 8 Then
    Dim numbers As String = "0123456789"
    Dim letters As String = "abcdefghijklmnopqrstuvwxyzöäüß"
    Dim numbers_Count As Integer
    Dim letters_Count As Integer
    For x As Integer = 0 To txtPasswort.Text.Length - 1
        If numbers.Contains(txtPasswort.Text(x)) Then numbers_Count +=1
        If letters.Contains(txtPasswort.Text(x)) Then letters_Count +=1
    Next
    If numbers_Count < 1 Then MsgBox("Das Passwort muss mindestens eine Zahl" & _
      "beinhalten",  MsgBoxStyle.Critical)
    If letters_Count < 1 Then MsgBox("Das Passwort muss mindestens einen" & _
    "Buchstaben beinhalten",  MsgBoxStyle.Critical)
Else
   MsgBox("Das Passwort muss mindestens 8 Zeichen enthalten!", _
     MsgBoxStyle.Critical)'oda so ähnlich.
End If