Option Explicit On
    Imports System.DirectoryServices
    Imports System.Net
    Public Class Form1
        Private Sub Form1_Load(sender As Object, e As EventArgs) Handles _
          MyBase.Load
            GetComputer()
            DomainSearcher(Environment.UserDomainName)
        End Sub
        Private Sub GetComputer() 'sucht alle compter in der domäne
            Dim result As String = ""
            Dim IPProperties As NetworkInformation.IPGlobalProperties =
                NetworkInformation.IPGlobalProperties.GetIPGlobalProperties
            Dim Domain As String = IPProperties.DomainName
            Dim DomainEntry As DirectoryEntry = New DirectoryEntry("WinNT://" + _
              Domain)
            DomainEntry.Children.SchemaFilter.Add("computer")
            For Each Computer As DirectoryEntry In DomainEntry.Children
                ListBox1.Items.Add(result & " | " & Computer.Name)
            Next
        End Sub
        Private Sub ListUsers(ByVal Item As String)
            Dim name() As String = Item.Split("|")
            'hier wird funktion, zum auslesen der benutzer aufgerufen
        End Sub
        Private Sub ListBox1_SelectedIndexChanged(sender As Object, e As _
          EventArgs) Handles ListBox1.SelectedIndexChanged
            ListUsers(ListBox1.SelectedItem)
        End Sub
        Sub DomainSearcher(ByVal Domain As String) 'soll benutzer in domäne 
        ' finden
            Dim Entry As New System.DirectoryServices.DirectoryEntry("LDAP://" _
              & Domain)
            Dim Searcher As New System.DirectoryServices.DirectorySearcher( _
            Entry)
            Searcher.SearchScope = DirectoryServices.SearchScope.OneLevel
            Dim Result As System.DirectoryServices.SearchResultCollection = _
              Searcher.FindAll
            For i As Integer = 0 To Result.Count - 1
                Dim newNode As New TreeNode
                newNode.Text = Result(i).GetDirectoryEntry.Username
                TreeView1.Nodes.Add(newNode)
            Next
        End Sub
    End Class

Gruß,
ZOMBI3