Option Explicit

Private Sub Form_Load()
    MsgBox "Suchtext in Zeile: " & ShowLine("E:\test.txt", "Beispieltext")
End Sub

Private Function ShowLine(ByVal xFile As String, ByVal xSuchText As String) As String
Dim FF As Integer
Dim xBuf As String
Dim xPos As Long
Dim xZeile As String

FF = FreeFile
    Open xFile For Binary As FF
        xBuf = Space(LOF(FF))
        Get FF, 1, xBuf
    Close FF

xPos = InStr(1, xBuf, xSuchText, vbTextCompare)
    If xPos = 0 Then
        ShowLine = xSuchText & " nicht gefunden!"
        Exit Function
    End If

xZeile = UBound(Split(Left$(xBuf, xPos), vbCr)) + 1

ShowLine = xZeile

End Function