Want to set apt pin-priority lower for none debian sites

[Florian Sukup <debian2005@sukup.at>]

Hi,

I want to assign a lower priority to packages which come from other 
sites than debian.org.

The problem: 
testing is my target release. In my sources.list there the following 
entries:

deb http://security.debian.org/ stable/updates main 
deb http://ftp.at.debian.org/debian stable main non-free contrib
deb http://ftp.at.debian.org/debian testing main non-free contrib
deb http://ftp.at.debian.org/debian unstable main non-free contrib
deb http://www.linex.org/sources/linex/debian sarge linex
...

# apt-cache policy mozilla-firefox
mozilla-firefox:
  Installed: 1.0.6-1.linex1
  Candidate: 1.0.6-1.linex1
  Version Table:
     1.0.6-5 0
        400 http://ftp.at.debian.org unstable/main Packages
 *** 1.0.6-1.linex1 0
        990 http://www.linex.org sarge/linex Packages
        100 /var/lib/dpkg/status
     1.0.4-2sarge3 0
        500 http://security.debian.org stable/updates/main Packages
        990 http://ftp.at.debian.org testing/main Packages
     1.0.4-2 0
        400 http://ftp.at.debian.org stable/main Packages

But this is not what I want. I want to have 1.0.4-2sarge3 0 installed. 
Automatically!

Does anyone know, if this possible (by changing the apt_preferences, for 
example).

I have tried a lot of ways, but no success.

Thank you for your help.

Florian.