<p>I'd like to be able to view the event <code>log</code> for a series of <code>asp.net</code> websites running on IIS. Can I do this externally, for example, through a web interface?</p>

Do you want to know if you can home-roll something or are you looking for an app you can get off the shelf?
I'm not a Windows guy, but I think Microsoft's MOM/SCOM solution will probably let you view the event log over a web UI - probably really heavy and expensive if that's all you need though.
A quick google found
http://www.codeproject.com/KB/XML/Event_Logger.aspx
which shows that you can get in if you want to roll your own... also an MS tool on
msdn
Sorry I can't be more help