Brisk

Well, it all depends on the type of server you want, but I've found rtcw.jolt.co.uk's guide to be great. As for setting up multiple servers, you can run multiple instances of the same ET.exe, or you can have separate installations (e.g on my clans server there's one ET directory "Wolfenstein - Enemy Territy" and another "Wolfenstein - Enemy Territory Pro"). Just make sure they're not running on the same port. ;)