Complete preferences file:
Package: *
Pin: release a=lenny-backports
Pin-Priority: 200
#----------------
Package: *
Pin: release o=apt-build
Pin-Priority: 989
#
Package: *
Pin: release o=volatile.debian.org,a=stable,l=debian-volatile
Pin-Priority: 988
#
Package: *
Pin: release o=Debian,a=stable,l=Debian-Security
Pin-Priority: 987
#
Package: *
Pin: release o=Unofficial Multimedia Packages,a=stable,l=Unofficial Multimedia Packages
Pin-Priority: 986
#
Package: *
Pin: release o=Debian,a=stable,l=Debian
Pin-Priority: 985
#
Package: *
Pin: release o=Debian,a=testing,l=Debian-Security
Pin-Priority: 99
#
Package: *
Pin: release o=Unofficial Multimedia Packages,a=testing,l=Unofficial Multimedia Packages
Pin-Priority: 98
#
Package: *
Pin: release o=Debian,a=testing,l=Debian
Pin-Priority: 97
#
Package: *
Pin: release o=Unofficial Multimedia Packages,a=unstable,l=Unofficial Multimedia Packages
Pin-Priority: 96
#
Package: *
Pin: release o=Debian,a=unstable,l=Debian
Pin-Priority: 95
#
Package: *
Pin: release o=Unofficial Multimedia Packages,a=experimental,l=Unofficial Multimedia Packages
Pin-Priority: 94
#
Package: *
Pin: release o=Debian,a=experimental,l=Debian
Pin-Priority: 93