The package manager for Debian is 'apt', or 'aptitude'.  You install new packages with 'apt-get install <package>'.  Alternatively, use 'aptitude', which is a gui-ish front end to apt.

Unfortunately, the Debian etch release, used in the deployed FOCE, is several versions out of date now.  The default configuration files for aptitude are configured to point at the current Debian release.  Thus 'apt-get' or 'aptitude' fails now.

The solution is to update the configuration files and the database.   The configuration file is at

/etc/apt/sources.list

By default, it contains lines that look like:

 deb http://linux.csua.berkeley.edu/debian/ etch main
 deb-src http://linux.csua.berkeley.edu/debian/ etch main

 You must add references to the debian archive, as follows:

 deb http://archive.debian.org/debian/ etch main contrib
 deb-src http://archive.debian.org/debian/ etch main contrib

When done, recompile the database with 'apt-get update'.