Can you give more details?
to see if you cam connect to mysql (you'll have to enter mysql's root password)
In mysql type
If you get a "database changed" message, then your database exists.
If everything is ok, type quit to exit mysql, then try:
mysql -u mail_admin -p
to see if the user you created for postfix works (you'll have to enter the password you set in the postfix configuration).
Apr 1 07:34:22 lightondesigns postfix/trivial-rewrite: fatal: proxy:mysql:/etc/postfix/mysql-virtual_domains.cf(0,lock|fold_fix): table lookup problem
This probably means there-s something wrong with the tables in your database. You could try to drop your database and redo the 4th chapter from the tutorial (Create The MySQL Database For Postfix/Courier).
To drop your database:
mysqladmin -u root -p drop mail