If you want to have the latest software for Debian, but you only want to upgrade some specific software, and not all your debian just follow this instructions
First, change to root
Then edit with your favorite text editor, (I use vi)
Mine looks this way, maybe yours look different.
#deb file:///cdrom/ sarge main deb cdrom:[Debian GNU/Linux 3.1 r3 _Sarge_ - Official i386 \ Binary-1 (20060904)]/ unstable contrib main deb http://mirrors.kernel.org/debian/ stable main deb-src http://mirrors.kernel.org/debian/ stable main deb http://security.debian.org/ stable/updates main contrib # Backports deb http://www.backports.org/debian/ sarge-backports main
That is all, but if you want to use backports only for selected packages, and not for all.
Edit or create the file /etc/apt/preferences
Explanation: see http://www.argon.org/~roderick/apt-pinning.html Package: * Pin: release o=Debian,a=stable Pin-Priority: 900 Package: * Pin: release a=sarge-backports Pin-Priority: 200 Package: * Pin: release o=Debian Pin-Priority: -1
Now, if you want a package from backports just do this.
#apt-get -t sarge-backports install foo
You can read all the explanation about this at: http://www.argon.org/~roderick/apt-pinning.html