if you`ve got a LAN at home it`s done without any problems. also, you can use multiple browsers and/or multiple UIs, but that`s trickier and usually pointless...
i think the user tracking part is done through http session tracking. if you can create multiple sessions on the same browser they should be treared as different users. supposedly, it`s just a hypothesis of mine...
btw, that`s why i`ve added that red flashing background for server name in my mods - i`m ususally tab-switching and i often used forms from another server by mistake. out of bp builds, things like that.
also, again on the mods (relevant only if you use them), i`m using a single global cache for data such as "empire name", "turns", "cash", "server" etc, so even if you faked your session id (assuming i was right with that hypothesis mentioned earlier in paragraph 2, of course) my mods would have problems...
regards
Anfit