[exim] [virtual user] config for exim4 in Ubuntu 12.04

Hy there,
I hope my question is not too booby :)
I am using exim4 on a semi productive system with physical users.

I want to setup a second server with exim4, courier and imapd with virtual users.

I was wondering if you can give me an example how to setup exim4 with the use of virtual users in Maildir format.
While searching on the i-net i found some examples, either using /var/mail/vdomain, /etc/exim4/vdomain, /home/user/vdomain and so on.
Is exim recommending a use case for virtual users with a salted passwd?

On top of that, I am searching for a web frontend, where users can create the user by themselves without the interference of an Admin. Can you help me with that?

I appreciate your time in advance!
Kind regards,
elrippo
--