1) Download et-linux-2.60.x86.run from: ftp://ftp.ulyssis.org/games/et/download/lin/et-linux-2.60.x86.run
2) Run this file as root or a normal user and install ET
3) Download the latest patch (2.60b): ftp://ftp.ulyssis.org/games/et/download/lin/et2.60blinux.zip 
4) Install this patch (unzip it, you will see a directory linux with 2 executables, overwrite the existing executables in the main ET dir.)
5) Download the extra maps and etpro from: ftp://ftp.ulyssis.org/games/et/download/common/maps-etpro.zip
6) Unzip this file in your main et directory, it will at the latest (3.2.5) etpro and the maps used on Ulyssis.