The apt-file command is amazing:
The apt-file command will tell you what Debian package owns any given file.
# apt-get install apt-file
# apt-file update
# apt-file search libg2c.so.0
It tells you which package includes a file that you need. It's been about 7 years since I used Debian, and after some really bad pain with apt-get upgrade, I swore off Debian and apt-get. Nowadays, I use yum and apt-get all the time with Fedora Core, and after learning about apt-file, I think it might be time to finally switch back to Debian.
So, I started with Slackware, first on a whole stack of 3 1/2" floppies, then on CD. Then I went to Red Hat for some time, then Stormix and Debian, then back to Red Hat and then to Fedora Core. For a while I flirted with a bunch of other custom distros, and used SuSE to get my laptop wireless card working. Now, it might be time to go to Ubuntu.
