Mail SETTINGS, not the actual mail messages, will sync with .Mac, but it will not sync the actual mail messages. That has to come from the email server on each of the accounts you're using.
You can have all mail messages on each computer, but how to do so depends on the kind of mail accounts (Imap or Pop). If POP, then in the account settings for each mail account (e.g., bellsouth, gmail, godaddy, etc.) tell it to leave the mail on the server for 30 days or so. That way, when you log onto the mail accounts from different computers (within 30 days) it will download all messages (and each computer will have all messages).
IMAP, I believe, does this automatically (the way your work email does it for most companies). Most "consumer" email accounts are POP -- the .Mac mail account, however, is IMAP I believe.
BTW, there's a program called SyncTogether that essentially does the sync'g that .Mac does, and it costs around $50 (a one-time fee for a 3 user license). I've been using it for almost a year and it works well to sync iCal, Address Book, Mail settings, Safari settings/bookmarks, etc. I liked .Mac but couldn't justify the $100 per year per user fee for what it gives you.
