What you should know about GNU/Linux chess software
eboard and XBoard are basically programs who displays the chess board. They let you play against various computer chess engines or a local or remote human adversary. The chess engines do the work, the front-end interfaces just show their output.
 The Interfaces
eboard is a more advanced version of XBoard. It is available for all GNU/Linux distributions. It is the logical choice.
XBoard is a very old chess interface. It's not very fancy, or flashy, but it has all the basic features of a modern chess program: You can play against all commonly used chess engines and connect to Internet chess servers.
Knights is a very nice KDE chess game. The last version (0.6.4-beta) was released in January of 2005. Development seems to have stalled. It supports themes, loading and saving of games, chess engines and Internet chess servers. It's the best chess interface available today.
Gnome Chess is/was a GNOME chess interface which was last updated in January of 2001. It's GNU, and the source is out there, so someone could possibly make a Gnome 2.x version and update it. It's not worth considering if you just want to play chess.
Slibo is a OpenGL 3D chess interface for KDE which could have turned out to be the coolest Chess engine in the universe. The project is very dead at this point and the last version (0.4.4) was released in August 2003. It doesn't compile against KDE 3.5, and this won't be fixed since the project is dead and unmaintained. Again, the source code is there, it's likely interesting and has value to programmers, but it's not a choice if just want to play some chess.
PyChess is a gnomebased chessclient written in python. It's GPL and is very much alive as of November 2007. The goal of PyChess, is to provide a fully featured, nice looking, easy to use chess client for the gnome-desktop. It has got a rich animated interface, with features such as internetplay over FICS and supports the xboard cecp engine protocol as well as the uci protocol.
 Humans are more fun!
The first thing you should do when you run eboard is to connect to FICS. Go Peer and Connect to FICS'. Login as "guest" with password "guest" to try it out. You will be able to seek an opponent and get one within seconds.
Humans with registered nicknames on FICS have a rating and this rating is shown. The higher rating the more resistance. Resistance seems to be futile if the opponent has a rating of 1800+.