First, Java is definitely NOT a huge waste of time. Anything you learn from any language can usually be applied in some way to another. And knowing more than one language is very useful. As far as XNA though, I started with this tutorial series when I decided to do a Ludum Dare using XNA. I had never used C# nor XNA, and started these tutorials about a week before the event. I didn't finish the game, but it was a 2D platformer that was mostly complete. It had enemies, shooting, scrolling levels, and collision detection anyways, haha.