Just go to the PBW site...
http://seiv.pbw.cc
... and sign up.
After that you can join any open game. Either one not yet started or one in progress looking for a replacement player.
Good luck and enjoy!
Oh, completely off topic: What does the " .cc " mean in the address? I've seen .com, .org, .edu etc. as well as country suffixes like .ca, .de, .au, but this is the only time I've seen .cc.