Override "created_at"-like Methods and add new one's


i'am about to redevelop an existing application and iam not allowed
to touch the structure of the database. Every table of the
database has the following fields:

anl_dat (<- created_at)
anl_user (<- who created the entry)
aend_dat (<- updated_at)
aend_user (<- who updated)

how can i override the default rails behaviour so it uses
the anl_dat instead of created_at?
and is there a way to tell rails to automaticly fill anl_user with
something like session[:user_name] ?

I need this for 99% of my models, only 2 tables
need special treatment...

Thanks in advance,