[Exim] Aliasing or Forwarding for non-user mail accounts?

As I'm sure everyone knows by now, I am a unix newbie and I am serving mail
to people who don't have accounts on my local box. I have a few questions
/ desires:

1. Could I get some advice (or chapter numbers :) on how I would go having
e-mail from one e-mail account sent to another instead? Either in the same
virtual domain or a seperate one?

2. How could I go about setting up some sort of Postmaster account where
mail to non-existant addresses goes? Could I be really kewl and just have
the Subject To and From sent to the Postmaster with some way of unfreezing
and delivering the full message to him if he wanted? Could I have a
seperate Postmaster per domain?

Thanks for the advice.

Daniel E.