'// Aufruf:
     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
       System.EventArgs) Handles Button1.Click
        Dim arr As New ArrayList
        Dim sr As IO.StreamReader
        Dim s As String
        Dim r As System.Text.RegularExpressions.Regex
        Dim searchWord As String = Me.TextBox1.Text
        Dim matches As Integer
        Const MAX_FILE_SIZE As Integer = 1024 '// Grösse der Datei beachten ( 
        ' 1MB)
        Me.GetFiles("C:\", "*.txt", arr)
        Me.ListBox1.Items.AddRange(CType(arr.ToArray(GetType(String)), String( _
          )))
        Application.DoEvents()
        For Each f As String In arr
            If New IO.FileInfo(f).Length <= MAX_FILE_SIZE Then
                Try
                    Me.Text = f
                    sr = New IO.StreamReader(f)
                    s = sr.ReadToEnd '// du könntest die Datei auch mit 
                    ' sr.ReadLine() einlesen. (wg. Speicherverbrauch)
                    sr.Close()
                    r = New System.Text.RegularExpressions.Regex(searchWord)
                    matches = r.Matches(s).Count
                    If matches > 0 Then
                        Me.ListBox2.Items.Add(f + " - Treffer: " + _
                          matches.ToString)
                    End If
                    s = String.Empty
                    Application.DoEvents()
                Catch ex As Exception
                    Me.ListBox2.Items.Add("Fehler beim einlesen der Datei: " + _
                      f)
                End Try
            End If
        Next
        arr.Clear()
        arr = Nothing
    End Sub
    Sub GetFiles(ByVal path As String, ByVal pattern As String, ByRef arr As _
      ArrayList)
        arr.AddRange(IO.Directory.GetFiles(path, pattern))
        For Each s As String In IO.Directory.GetDirectories(path)
            GetFiles(s, pattern, arr)
            Application.DoEvents()
        Next
    End Sub