prova così:
dim testo as textbox
Public Sub Savetxt(path As String, stringa As TextBox)
Dim myrecord As String * 1
a = Len(stringa.Text)
Open path For Binary As #1
For i = 1 To a
stringa.SelStart = N
N = N + 1
stringa.SelLength = 1
myrecord = stringa.SelText
Put #1, N, myrecord
Next i
Close #1
End Sub
Private sub command1_click()
testo.text = text1.text & text2.text
Savetxt "C:\tuopercorso.txt", testo
end sub

ciao!!!