[Dovecot] per user quota

Hi, i've tryed to setup per user quota with postfix/dovecot, but
without luck. My configuration is:

postfix 2.3.8 with virtualdomain on mysql (http://workaround.org
tutorial) dovecot 1.0.9

IMAP/PO3 OK on dovecot config, i've made the changes for the quota plugin, i've setup the gereral quota at 20MB, with this configuration:

quota = maildir:storage=20480:messages=1000

it works very well, from telnet connection and squirrelmail, i see the
right % of quota used.

My problem is the per user quota, if i want give some user, more or
minus space, i'm not able to do this.

I've added a quota field to the mysql that read dovecot, but i don't
know ho to read this in dovecot-mysql.conf.

Someone can help me?

Thanks