My current mail setup is exim4 * forwards my email for domains and sub-domains to my google address (and i do the same for a couple people as well). I am now trying to fully host it on my Debian Squeeze server.
I installed Cyrus and Squirrelmail via dselect. There were no configuration options displayed. What do i do next? Is there some configuration tool?
Well, here are the Exim wiki instructions for Cyrus: http://wiki.exim.org/CyrusImap i.e., Exim talks to Cyrus via LMTP.
Mailbox setup for Cyrus is via the cyradm tool (not sure how it's packaged on Debian). You'd create the mailboxes, grant privs for users, etc. Some basic docs are here: http://oreilly.com/catalog/mimap/chapter/ch09.html or http://nakedape.cc/info/Cyrus-IMAP-HOWTO/maintenance.html
Cyrus itself should be configured to listen on 993 publically (for SSL) and perhaps localhost:143. It should spawn an LMTP listener, for Exim delivery. There are perhaps some other ancillary services you can start up also, depending on what you're doing.
The squirrelmail bit is pretty simple. You'd set up squirrelmail so that you're pointing at, say, localhost:143. There are also some SMTP options you would set to point at your local Exim, if that's configured to send mail.
