[imp] quota driver sql

[jotace]

I am configuring horde/imp with quotas, but i have some problems.
I have horde 3.0.4 / imp 4.0.2 / mysql 4.0.24 / postfix / dovecot / apache2 on 
debian sarge, I have users on my database but I have some problems with quotas.
I use postfix and dovecot, i put the quota of 10 MB. What can i do to show 
user's quota if the users are stored in a database (mysql)?
This is my table mailbox, :
select username, home, maildir, quota, domain  from mailbox;
 
+-------------------------+------------------+-------------------------+-------
------+--------------+
| username                 | home              | maildir                     | 
quota       | domain       |
+-------------------------+------------------+-------------------------+-------
------+--------------+
| test at domain.com      | /home/vmail/  | domain.com/test/     | 10240000 | 
domain.com |
| test2 at domain.com    | /home/vmail/  | domain.com/test2/   | 10240000 | 
domain.com |
| test3 at domain.com    | /home/vmail/  | domain.com/test3/   | 10240000 | 
domain.com |
+-------------------------+------------------+-------------------------+-------
------+--------------+

I know that in the cvs version, there is an sql based quota driver for imp.
How can i use this sql driver to use or adapt to my configuration and configure
it for my sql setup. 

Thanks for your help.