yum update question

[Rainer Traut]

Hi,
I have a question about yum,
let's say I have 2 repositories in yum.conf,

e.g.
base and updates-released for my fedora.

Cron job is running over night and installs the updates fine.

But what do I have to do if I fill in yum.conf another big repository
e.g. from Dag Wieers.
It is updating many packages which I do not want to, because I only need 
two or three of his repository?!

Is there a way to exclude one repository from yum update ?
A flag in yum.conf would be nice, to not use this entry for yum update?!

Thank you
Rainer