How to Authenticate users NT server password?

I'm using VB5, and want to know what API or coding I need to Authenticate NT user account passwords in Visual Basic. The below code was generated using the VB Application Wizard, when prompted if I wanted a logon in my application.

Private Declare Function GetUserName Lib "advapi32.dll" Alias "GetUserNameA" (ByVal lpbuffer As String, nSize As Long) As Long


Public OK As Boolean
Private Sub Form_Load()
Dim sBuffer As String
Dim lSize As Long


sBuffer = Space$(255)
lSize = Len(sBuffer)
Call GetUserName(sBuffer, lSize)
If lSize > 0 Then
txtUserName.Text = Left$(sBuffer, lSize)
Else
txtUserName.Text = vbNullString
End If
End Sub





Private Sub cmdCancel_Click()
OK = False
Me.Hide
End Sub


Private Sub cmdOK_Click()
'To Do - create test for correct password
'check for correct password
If txtPassword.Text = "" Then
OK = True
Me.Hide
Else
MsgBox "Invalid Password, try again!", , "Login"
txtPassword.SetFocus
txtPassword.SelStart = 0
txtPassword.SelLength = Len(txtPassword.Text)
End If
End Sub



Thanks,