Buy it here as Gamers Gate does not include Curse of Souls and here its DRM Free.
I see. Thanks for the reply. :) I wanted to buy it with Blue Coins, but I guess I'll wait for some other game.
As far as I remember, all the "expansions" for Two Worlds were included in patches. So as long as the GamersGate version is patched to the latest build, it should have all the same content as any other version.
So if you want to double check that, either ask their support or ask via Twitter. As long as it's version 1.7b or higher (or has that patch available), it's got Curse of Souls included. But bear in mind, that content is only available in the Multiplayer mode.