You must be running Quake3 1.17

Coliseum2 Mod is based on the 1.17 source code.

Create a directory under your main quake3 directory
called coliseum.

Unzip the download put all the PK3 files into that directory.
Also put the file called description.txt into that directory.

Start Quake3 and goto the MODS menu and you should see Coliseum2
listed there.  Highlight it and click Load.

HTML documents are contained in the docs directory included with this download.

WarMonger
www.planetquake.com/coliseum2