I would prepare by writing programs to do useful things or play games...
What language is the course based on? and what programming environment do they use? Knowing this will help you get a headstart.
If its Java and you don't know then I'd suggest checking out Processing at processing.org. There are many examples to try out and the programming
model is very easy to learn and from there you can explore java and programming concepts using graphics as a starting point.
If they use Eclipse IDE or NetBeans IDE then download these tools, install them and find a tutorial to learn how to use them for development.
If you have a scientific interest then there is the Open Source Physics collection of Java programs at
www.compadre.org/osp
If you have a comparative programming languages interest then there is
www.rosettacode.org where various programming tasks are solved using a multitude of programming languages.
Computer science is not about knowing many languages but knowing a few really well and knowing how to use them to solve a problem.