This portable version of Quake III Arena was created with Thinstall. It allows you to play the game from a USB drive on any compatible computer. It was tested on XP and Vista, but it should also work on Windows 98. A 200 MHz+ CPU is required (1 GHz+ is recommended).
I included the ability to add arenas without loosing portability (they're copied to the 'Q3Settings' folder, along with all other settings and modifications).
Lastly, since it's portable, you can play it while seeding, SO PLEASE SEED!, at least to a ratio of 1. Enjoy.
(fixed) The file browser I previously included for adding your own arenas modified files simply if they were selected (set flags), and consequently, if you accidentally selected the game's system files they were copied to the Q3Settings folder, potentially doubling the app's size. :(