Public Shared Function UserExists(ByVal username As String) As Boolean
Dim de As DirectoryEntry = GetDirectoryEntry()
Dim searcher As New DirectorySearcher()
searcher.SearchRoot = de
searcher.Filter = String.format("(&(objectClass=user) (cn={0}))", username)
Dim results As SearchResultCollection = searcher.FindAll()
Return results.Count > 0
End Function