The Linux installer is included on Disc 3 of the 3 CD set! We support both client and server for Linux. Unfortunately there’s no mention of Linux on the box because we didn’t know it would be done in time so please tell all your Linux gaming friends that UT2003 is ready for them!
In the meantime, you can still grab the Linux demo (and patch) from here. Thanks to all the people who wrote in with this news.