Comment 29 for bug 624877

FWIW, here is the command set for what I'm doing on my Lucid systems:

# make it so that lucid packages have default priority over natty ones
cat << EOF > /etc/apt/preferences.d/prefsources
Package: *
Pin: release a=natty
Pin-Priority: -10

Package: *
Pin: release a=lucid
Pin-Priority: 900
EOF
# create a natty sources list based on the existing lucid list
grep ^deb /etc/apt/sources.list|sed 's/lucid/natty/' > /etc/apt/sources.list.d/natty.list
# double the default apt cache limit to allow for more/larger repositories
echo 'APT::Cache-Limit "50331648";' > /etc/apt/apt.conf.d/98cache-limit
# issue an apt-get update to cache the new repository
apt-get update
aptitude -y install dpkg/natty
echo "force-unsafe-io" > /etc/dpkg/dpkg.cfg.d/force-unsafe-io

As for the best course of action on killing dpkg, it goes into a D state (uninterruptible sleep) and won't respond to even a kill -9. To get it gone, a couple of your options: wait for all the filesystems to finish syncing (reducing filesystem activity will expedite it), or reboot the system.