I've just installed Ubuntu this night, however starting WoW will give me a directx error.
I have installed DirectX through the normal installer and through/with CrossOver.
How can this be resolved? Thanks in advance.
Try installing WoW through playonlinux (which you can find in the default repositories or here). If that does not help, have a look at the WineHQ database concerning WoW. In both cases, make sure that you are using Wine >=1.3.x.