The Wiki has its own login/registration. Under the Wiki Login box on the right, there is a place to register for the Wiki, then log in. I suggest you use your forum display name to register and the same password you use for the forum (less to remember).
By the way, the Wiki is having a problem right now which I hope to get fixed soon...for some reason it will not allow people to save new pages or save edits to existing pages. Some sort of permissions problem I am trying to figure out.