the way to open two clients for every mmo that i found is to make two windows users.
When u have and ur on first one dont log out, just swich users and log on second one (when games are running there is no way to logon another windows user, atleast on XP)
Now on u can run one client per windows user
Ps. on 2moons its working but after swich i mostly get dc at previous user. But its maby cuz my mashine is old (amd 1,4ghz, 512 ram, gf5200)