Hey budy,
Okay, step by step, before we start, we should try to find out what we wanna do here.
Otherwise you ll spend your money on expensive software and find out that it isn’t doing what you want it to . . .
As I can see it you have a pefect rig, why not animate it in Maya???
Otherwise:
To get your character into MB you ll have to follow a specific structure of how to build and label your joints. http://atec.utdallas.edu/midori/Handouts/motionBuilder_character_files/joint_names.jpg
Once your skeleton is built and you bound the goemetry import your character into MB and characterize it, the step that builds the rig for you. 3dbuzz.com has a great tutorial on how to do all that.
Now all you need to do is happily animating.
When you are done with that, plot your character and export it via fbx (there is an advanced tecnique using the FBIK rig in maya, but try this first)
That’s all there is to it.
http://atec.utdallas.edu/midori/Handouts/motionBuilder_character.htm
here is a great link, where all the steps are explained in more detail. Hope that helps