One way would be to have the After Update event for the text box bound to
the Notes field contain something like:
Me.NoteWriter = CurrentUser()
where NoteWriter is the text field in which the user who who wrote the note
is recorded. You may need to do something to lock the control after the
note has been added, or the CurrentUser will become the last person who
edited the information. Logging in as a particular user, as mentioned in
another reply, is what will make this work. Implementing User Level
Security is one way. Search for that term and you should get all sorts of
links and other information. This page contains links to several helpful
sources:
http://www.jmwild.com/Accesssecurity.htm