[horde] Horde SQL Authentication with Postnuke....?

[Hugo Proost]

Can anyone please tell me if the following is possible with Horde...and
if so how?
 
I host a Postnuke 7.2.3 powered site with its own MySQL database and its
own (Postnuke)users. 
I also run an experimental Horde site on that same server with its own
database and its own(Horde)users.
 
Now I was wondering if it would be possible to let Horde authentication
look at the Postnuke MySQL database. I want to prevent users that have
already been authenticated by Postnuke from having to fill in there
username and password again if the want to enter Horde.
 
I saw a couple of Authentication files in the folder 'horde\lib\Auth'
but I am not that educated in the art of PHP 
 
By the way, I am using:
 
- Windows XP
- Apache 2
- PHP 4.3.0
- MySQL 3.23
- Horde 3.0 cvs
- And some other stuff for Horde
- Postnuke 7.2.3
 
MANY THANX,
Hugo