We're just evaluating bullet to integrate it in our multiplatform inhouse game engine. How can we access the Wii and Xbox360-version. We're already registered for the PS3 version.
As far as I know, there is no Wii/360 version, as there is a PS3 version. Integration with the Wii is exceedingly simple, and I'd be surprised if it's any more difficult to get it running on the 360.
Yes, porting Bullet to a new platform is pretty easy. You just need to throw all the source into a project, and go through btScalar.h adding implementations for your compiler.