How Can I Get The Logon Name?

I'm using Basic Authentication for my web site - not great I know but I'm
having to support devices like the Nokia 9210i which dosn't seem to like the
digest information for windows domain servers.

The question is that I would like to be able to somehow capture that logon
username/id so that I can use it within the web site to track changes made
by the user.

I've thought about switching off authentication all together
and writing my own logon asp page (query to an SQL database or something and
then store the result in a session variable), but if I can somehow capture
and access the basic authentication information, it would save me some work.