All lines that start with a '#' are comments

============ Edit /etc/apt/sources.list =====================

# add two new lines, to list the "testing/lenny" repos

# deb http://http.us.debian.org/debian testing main contrib non-free
# deb-src http://http.us.debian.org/debian testing main contrib non-free

# NOTE: those two URLs above need to be corrected to list the actual repos
# You should likely use the repos you already have.

============= Make a /etc/apt/preferences file and populate it =============

Package: *
Pin: release a=stable
Pin-Priority: 900
Package: *
Pin: release a=testing
Pin-Priority: 100