I personally would recommend that you wait until you start learning stuff in class before you try doing anything on your own. Unguided learning in programming can be difficult to do well, and it has the pitfalls of leading to bad habits/mentality when you actually *do* get around to learning properly from someone.
That said, if you want to get a head start, it definitely doesn't hurt to learn some core fundamentals. Given your timeframe, I think the best thing you can do now is to familiarize yourself with some basic programming concepts rather than a particular language.
I've been recommending this to others wanting to do self-learning:
http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-00-introduction-to-computer-science-and-programming-fall-2008/Of course, it won't hurt to learn some basic hello-world-esque stuff in C++ before going into your class, but it really doesn't give you a good sense of what programming/software engineering really is about.