ma questa dll che autentica il login si trova sul server o sul client?
se si trova sul server

codice:
'codice da inserire in un progetto dll activeX
'nome della classe clsLogin
'nome del progetto Login
Option Explicit

'variabili private
Private m_UserName As String
Private m_PassWord As String
Private m_Conn As ADODB.Connection
Private m_Rs As ADODB.Recordset
Private m_loginOk As Boolean

Sub ConnectDB()
   Dim sSql As String
   Set m_Conn = New ADODB.Connection
   With m_Conn
      'tipo di cursore
      .CursorLocation = adUseClient
      'stringa di connessione
      .ConnectionString = "Provider = microsoft.jet.oledb.4.0;" & _
      "persist security info = false; data source = c:\pws-gest.mdb"
      'modo di accesso ai dati
      .Mode = adModeReadWrite
      'apertura database
      .Open
   End With
   Set m_Rs = New ADODB.Recordset
   
   sSql = "SELECT * FROM pass WHERE username = '" & Me.Username & _
      "' AND password = '" & Me.Password & "'"
   m_Rs.Open sSql, m_Conn
   If m_Rs.RecordCount > 0 Then
      m_loginOk = True
   Else
      m_loginOk = False
   End If
   m_Rs.Close
End Sub

Private Sub Class_Initialize()
   Me.Username = "%"
   Me.Password = "%"
End Sub

Property Get Username() As String
   Username = Trim(m_UserName)
End Property

Property Let Username(ByVal sValue As String)
   m_UserName = Trim(sValue)
End Property

Property Get Password() As String
   Password = Trim(m_PassWord)
End Property

Property Let Password(ByVal sValue As String)
   m_PassWord = Trim(sValue)
End Property

Property Get LoginOK() As Boolean
   LoginOK = m_loginOk
End Property
per provarlo

codice:
Option Explicit
'codice da inserire in un exe standard
' ridorda di inserire la tua dll nei riferimenti
Dim Log As login.clsLogin
Private Sub Form_Load()
   Set Log = New login.clsLogin
      Log.Username = "xegallo"
      Log.Password = "ciccio"
      Log.ConnectDB
      MsgBox Log.LoginOK
End Sub