Here's some code to find all the computers in a domain...not exactly what you were looking for, but no DLL required, either...

Code:
Public Function GetComputersInADomain(aryUsers() As String) As Long

    'Notes:  Requires a global array to be pased in if list of users wanted
    'Notes:  Very slow if domain name not valid
    'Notes:  Must set reference to Active DS Type Library for this to work
    
Dim TheDomain As IADsDomain
Dim Computer As IADsComputer
Dim strDomain As String
Dim x As Long

    'Accept the Domain name
    strDomain = InputBox("Domain Name: ")

    'Use the WinNT Directory Services
    strDomain = "WinNT://" & strDomain

    'Create the Domain object
    Set TheDomain = GetObject(strDomain)

    'Search for Computers in the Domain
    TheDomain.Filter = Array("Computer")

    'Enumerate each computer in the domain
    For Each Computer In TheDomain
        x = x + 1
        ReDim Preserve aryUsers(x)
        aryUsers(x) = Computer.Name
    Next Computer

    'Clean up
    GetComputersInADomain = x
    Set Computer = Nothing
    Set TheDomain = Nothing

End Function