...anche se è tardi...
l'avevo fatto col do:
codice:
Const FileName = "C:\File.txt"
Dim Riga As String
Dim TestoFinale As String

Open FileName For Input As #1
  Do Until EOF(1)
    Input #1, Riga
    Do Until InStr(1, Riga, "idad=") = 0
      If InStr(InStr(1, Riga, "idad="), Riga, "&") <> 0 Then
        TestoFinale = TestoFinale & Mid(Riga, InStr(1, Riga, "idad="), InStr(InStr(1, Riga, "idad="), Riga, "&") - InStr(1, Riga, "idad=") + 1) & vbCrLf
      End If
      Riga = Right(Riga, Len(Riga) - InStr(InStr(1, Riga, "idad="), Riga, "&"))
    Loop
  Loop
Close #1