Option Explicit
Sub Test()
Dim strFilename As String
Dim strUser As String
Dim s As Long
Dim e As Long
strFilename = "C:\Dokumente und Einstellungen\b0053940\NTUSER.DAT"
e = InStrRev(strFilename, "\", Compare:=vbBinaryCompare)
s = InStrRev(strFilename, "\", e - 1, Compare:=vbBinaryCompare)
If s < e Then strUser = Mid$(strFilename, s + 1, e - s - 1)
Debug.Print "User: " & IIf(strUser <> "", strUser, "<not_found>")
End Sub