Reading Active Directory by VB.NET Source code...

''' <summary>
''' This is the friend class which used to manage daomain login.
''' </summary>
''' <remarks></remarks>
Friend Class LoginManager
Friend Shared Function Authentification(ByVal username As String, ByVal pwd As String) As Boolean


Dim entry As New DirectoryEntry("LDAP://" & Environment.UserDomainName, username, pwd)

Dim obj As Object
Try
obj = entry.NativeObject
Dim search As New DirectorySearcher(entry)
Dim result As SearchResult
search.Filter = "(SAMAccountName=" + username + ")"
search.PropertiesToLoad.Add("cn")
result = search.FindOne()
If result Is Nothing Then
Return False
End If
Catch ex As Exception
Return False
End Try

Return True
End Function
End Class