It's pretty simple. There is a install program on the Ut2004 disk for Linux. I forget exactly were it's located and such, but it shouldn't be to hard to find.
run that script, it will start a install GUI. Install the software.
Then you should be able to run the program and activate it with the cd key, and play with it.
If you want the latest update they are in the form of simple tarballs. These are like zip files, but are the standard for unix-like systems. You untar the tarball in a seperate directory.. take a look at it to make sure that it's ok.. then you just copy the contents of that directory over the ut2004 install directory to replace the various files and folders with the updated versions.
I remember there was a issue some people ran into with certain updates were the cd key wasn't be accepted by the activation servers... I think this was due to a bug with the servers on how they interpreted the 'carrage return' symbol at the end of the text file.. the fix for this is to find the file were the cdkey is stored and edit it slightly and save it.
What I found usefull for ut2004 is when you finish the fresh isntall, and if you have plenty of disk space, make a backup copy of the installation directory. So if you want to run beta patches or if you make a mistake and break the program for a update you can delete the install and copy the back up directory to the installation location. It's much easier/faster then having to sit through the multi-cd install again.
if your running 64bit Linux you can get a native ut2004 version for that. It's been around much longer then the 64bit windows version. I don't know if it has a install for that included with the cdrom.
For id games, like doom3 and quake3 you can go to their ftp website, ftp.idsoftware.com, and download the game/game isntaller (called point releases) from there. All you need then is the pak files off of the cdroms and the cdkey. Wolfenstien and such are the same way.
You can even get the source code if you want to try at recompiling it. Quake3 has been GPL'd. (the artistic content is still restricted and you require a retail copy of it for that).
Distros like Debian or Ubuntu should have optimized/modified versions of Quake 1 and 2 aviable... like quake3/doom3 you'd have to copy the package files to the correct directories.
You can find more information on several websites.
http://www.linux-gamers.net/
has some ut2004 information (and performance tweaks and such) and articles link to special isntallers and stuff you can use for ut2004 updates and a few mods.
The guy that runs this website is responable in a large way for the ports of UTxxx and Ameria's Army. He has a lot of good information on games and such for Linux.
http://icculus.org/lgfaq/
http://icculus.org/
doing searches for 'linux games' or linux gamers and such can find you lots of good detailed information.
edit:
If possible always keep up to date on the latest versions aviable for the paticular distro your using. It makes things much easier and upgrades thru using the cdrom installer are usually very successfull, unless you have a lot of 3rd party rpms installed.
Although Fedora Core 5 will be coming out in not to much longer, so it may be easier to way for a few weeks or a month or so after that is out (so more advanced users get the initial bugs shaken out and documented) before upgrading. (FC5 is due out at the end of next February.) New releases are done every 6-8 months.
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