As already posted on planet ubuntu, do not forget to attend this lesson if you want to learn an usual way to update a package, how to avoid typical traps, plus some additional hints and hidden bonus points :)
If you want to follow the session and practice a little, it's better that you get some downloaded packages:
sudo apt-get install build-essential devscripts ubuntu-dev-tools debhelper diff patch quilt fakeroot lintian libtool gnome-common gnome-doc-utils gtk-doc-tools
You should also have "deb-src http://archive.ubuntu.com/ubuntu/ jaunty main restricted" in your /etc/apt/sources.list (and then sudo apt-get update).
Ready? The session is scheduled for: 16th April, 18:00 UTC, and it will take place in #ubuntu-classroom on irc.freenode.net.