Apis's

Perdón por la demora, tuve mucho trabajo, he leído tu mensaje y por lo general yo uso 2 funciones apis, que es GetUserName (usuario) y WNetVerifyPassword (contraseña), pero traté de usar LogonUser, bueno te mando 2 ejemplos:
En un módulo pegá:
Option Explicit
Declare Function GetUserName Lib "advapi32.dll" Alias _
"GetUserNameA" (ByVal lpBuffer As String, _
nSize As Long) As Long
Private Declare Function WNetVerifyPassword Lib "mpr.dll" Alias _
"WNetVerifyPasswordA" (ByVal lpszPassword As String, _
ByRef pfMatch As Long) As Long
Public Function GetWindowsLoginUserID() As String
Dim rtn As Long
Dim sBuffer As String
Dim lSize As Long
sBuffer = String$(260, Chr$(0))
lSize = Len(sBuffer)
rtn = GetUserName(sBuffer, lSize)
If rtn Then
sBuffer = Left$(sBuffer, lSize)
If InStr(sBuffer, Chr$(0)) Then
sBuffer = Left$(sBuffer, InStr(sBuffer, Chr$(0)) - 1)
End If
GetWindowsLoginUserID = sBuffer
Else
GetWindowsLoginUserID = ""
End If
End Function
Public Function VerifyWindowsLoginUserPassword _
(ByVal Password As String) As Boolean
Dim rtn As Long, Match As Long
rtn = WNetVerifyPassword(Password, Match)
If rtn Then
VerifyWindowsLoginUserPassword = False
Else
VerifyWindowsLoginUserPassword = (Match <> 0)
End If
End Function
crea un formulario y colocá do textbox y un commandbutton:
Private Sub cmdVerify_Click()
MsgBox "la password administrada es: " _
& VerifyWindowsLoginUserPassword(txtPassword.Text)
End Sub
Private Sub Form_Load()
txtUsername = GetWindowsLoginUserID
txtUsername.Enabled = False
End Sub
usa tu imaginación para cargar los nombres com quieras.
' función LogonUser
'crea un formulario con uncommandbutton
Private Declare Function LogonUser _
Lib "Advapi32" Alias "LogonUserA" _
(ByVal lpszUsername As String, _
ByVal lpszDomain As Any, _
ByVal lpszPassword As String, _
ByVal dwLogonType As Long, _
ByVal dwLogonProvider As Long, _
phToken As Long) As Long
'Sólo para win95,WinNt
Private Const LOGON32_PROVIDER_DEFAULT As Long = 0&
Private Const LOGON32_PROVIDER_WINNT35 As Long = 1&
Private Const LOGON32_LOGON_INTERACTIVE As Long = 2&
Private Const LOGON32_LOGON_NETWORK As Long = 3&
Private Const LOGON32_LOGON_BATCH As Long = 4&
Private Const LOGON32_LOGON_SERVICE As Long = 5&
Public Function Login(ByVal xi_strUserID As String, _
ByVal xi_strPassword As String) As Boolean
Dim p_lngToken As Long
Dim p_lngRtn As Long
p_lngRtn = LogonUser(lpszUsername:=xi_strUserID, _
lpszDomain:=0&, _
lpszPassword:=xi_strPassword, _
dwLogonType:=LOGON32_LOGON_NETWORK, _
dwLogonProvider:=LOGON32_PROVIDER_DEFAULT, _
phToken:=p_lngToken)
If p_lngRtn = 0 Then
Login = False
Else
Login = True
End If
End Function
Private Sub Command1_Click()
Dim Resultado As Boolean
Resultado = Login("User", "Pwd")
MsgBox "EL RESULTADO DE LA PASSWORD ES:" & Resultado, vbInformation, "ACCESO"
End Sub

Ya te lo he mandado otra vez.

Tal como lo cuentas no entiendo para que necesitas la contraseña, ya que si sabes el usuario actual, este usuario ya se habrá autentificado.
Por otra parte aunque no estoy muy puesto en el tema de las apis, lo de phtoken me suena a algo del tipo de red.