To extract .pak files from Quake, see Section (2.1 Getting Started) of:
  http://tldp.org/HOWTO/html_single/Quake-HOWTO/#ss2.1

Once the pak files are extracted, copy them to /usr/share/games/darkplaces/id1

If you don't own the game, you can use the "darkplaces_shareware_data" package 
available at SlackBuilds.org.

