whenever i try to join a server (server is running on Kubuntu Feisty) on my windows XP laptop, it does one of two things. it either shows me a "incorrect game directory" error and kicks me back to the main menu, or gets stuck at a "downloading map" screen, showing "downloaded 0 bytes of 0 bytes".
Sounds like A) you have an old version of Open Arena, upgrade to 0.7.0 and apply patch for 0.7.1 and B) the server/s you are trying to join are running modifications, or custom maps, enable autodownloads in order to enter such servers.