[girfan]

Take courses across a breadth of areas in Computer Science, even if you think you don't (or won't) enjoy them much. Don't take up courses only in areas you enjoy (say, Networking) and have no concrete knowledge of areas you think you don't really like (say, Graphics) - Undergrad in my opinion is ideal for building up breadth of Computer Science knowledge. You can always focus on specific areas in grad school or when you start working.