[Dovecot] dovecot: auth(default): Fatal: Unknown database driver 'mysql'

I just tried upgrading from 1.1.rc6 to v1.2.11, and am getting the following error: dovecot: auth(default): Fatal: Unknown database driver 'mysql'. If I change the respective line in dovecot-sql.conf from driver = mysql to driver = pgsql the error message changes accordingly: dovecot: auth(default): Fatal: Unknown database driver 'pgsql'.

I quit using 1.1.rc6 because it started choking on my Debian system, so I'm back to using the stable Debian version - 1:1.0.15-2.3+lenny1. Where are the drivers kept when I do a default build, and where in the configuration file does it tell dovecot to look for the drivers? Other suggestions on a fix?

Glen