Well, you're going to need to convert the model first using a 3D modeling app like Maya, XSi, or 3DS Max first. Google around for some guides and check out some sites like facepunch, fpsbanana, and garrysmod.
Protip: It's not easy to convert models... AT ALL. You're going to need to pour a lot of time and effort into that model to make it work properly. I think there's also a thread somewhere over at facepunch that deals specifically with N64/GC/Wii models. Last time I saw it, the ghosts from Luigi's mansion were dumped, but Luigi himself wasn't. The SSBB version was dumped a while back though.