Hi PNR,
Have you tried something like this ?
Dim sw As StreamWriter = New StreamWriter(server.mappath("myfile"))
sw.Write(Editor1.PlainText)
sw.Close()
It worked out ok for me.
Also, on IE6 / win2K I had to add permission to ASPNET user.
On IE6 / win2003server, it was not enough, I had to add permission to IIS and IWAM (although I still don't understand why).
Good luck !
julien