This is probably a bit late to vets of the PC gaming scene, but... Linux and Mac users can play Quake III via "io Quake 3".

1) Download the version of io Quake 3 for your OS (Win/Mac/Linux).
2) Copy the files in the "baseq3" folder from the GOG/Steam version of Quake III.
3) Paste the files into the "baseq3" folder in ioquake3.

Launch and enjoy!

io Quake 3 can be found here:
http://ioquake3.org/get-it/

Soooo, I'm trying to get started with Quake 3 on linux. But it's not that easy to extract the game files (baseq3) when you don't have a Windows machine :(

Any ideas?

Have you tried innoextract?

If you have Wine, simply install the Windows version via Wine. Then, got into the virtual c drive and skim thru Quake 3 to find the 'baseq3' folder. Then, copy those files into the 'baseq3' folder in the Linux version of ioquake3. That should work.

UPDATE:
Metal Tech v20 works with ioQuake3 on Linux Mint!
But, you must have Wine installed.

Metal Tech v20 mod can be found here: http://www.moddb.com/mods/metal-tech-v20-revolutions/downloads/metal-tech-v20-revolutions The installation instructions are en espanol.

After downloading MetalTechv20, do as so:
1. Launch MetalTechv20 via Wine.
2. Set your installation path.
3. Install path should be set to:
/
Home
ioquake3
baseq3

Enjoy!