UT2003 Community Bonus Pack for Linux
This is where you can get the UT2003 Community Bonus Pack installer for Linux.
The Digital Extremes Bonus Pack can be found here
The Epic Bonus Pack can be found here
Here's a shot of the installer:
Download the Community Bonus Pack Installer (md5sum).
The installer is approximately 130MB.
Run the installer as the same user you installed UT2003 as.