Just to be a little more technical on Marsd's comment they are different skins on the same WPN network, so yes seperate cardrooms but being on the same network you will not be able to have them both running at the same time.
You can sign up to both with no issues as long as your only playing on one of them at a time.
This same scenario holds true of the Merge network (carbon, pokerhost, aces (i think its something like that)), revolution network (juicy, intertops
, pure) etc. You can play on all skins but only one can be running on your computer for the network at the same time.