Well, I have the SCJP and it does not prepare you to build a game...
If you want to do a game with motion capture you must research about game programming a lot, and about motion capture and animations a lot... its not about java.... What I mean:
If you want to make a game you will not be focused in JAVA but in game programming... java will be just a tool...
Well.. I like the JavaMonkey Engine ( jmonkeyengine.org ) but you may have to build a way to use motion capture ( maybe using the JFM Library or build your own lib ).
If I can suggest another path: Try to build simple games, I mean.. 2d games with java if you just want to practice your java knowledge... take a look in a old book called Killer Game Programming in Java its a interesting book about java + game programming... you will learn some java facets and some game programming theory...
Good lucky with your SCJP exam!!
[]´s