Backports are recompiled packages from testing (mostly) and unstable (in a few cases only, e.g. security updates), so they will run without new libraries (wherever it is possible) on a stable Debian distribution.

I recommend you to pick out single backports which fits your needs, and not to use all backports available here.

Add this line

deb http://www.backports.org/debian/ sarge-backports main

to your /etc/apt/sources.list, and these lines

Package: *
Pin: release a=sarge-backports
Pin-Priority: 200

to your /etc/apt/preferences. That will _deactivate_ all packages from backports.org. To install a package (e.g. mutt), use

apt-get -t sarge-backports install mutt

or

apt-get install mutt/sarge-backports

if the previous command fails.

This is easier when the package requires additional backports.