Yes you need to register with the forums to access downloads other than the main GC2builder application. The site will have some nice exclusive content in the future, and it's a great forum for modders. I've put my custom models on hold until someone figures out how to get textures working ingame using Blender.
I'll be working on releasing the version two's now. You can see screenshots of the difference in the versions @ http://www.gc2builder.com/vtopic-93.html