Rails - Aug 2005 - Checking/modifying response before it's sent to user

I want to execute some code based on the status code of a response,
but before it gets sent back.  For example, if we''re sending back a
404, I''d like to log it, and perhaps change the status to a 200.

I *think* what I need to do is override Dispatcher.dispatch in my
environment.rb file.  But I''ve got no real clue how to say "Okay
the
response is a 404 now, let''s do ____".  Can anybody give me some
tips
on doing this?

Thanks, Pat