Don't install Napster, Kazaa, ChainCast, or any software from an unknown source. The former will turn your computer into a server and the latter may contain trojans and viruses.
Turn off sharing, especially on your C:\ and D:\ drive. This is very dangerous! If you must share a disk, make sure it requires a password. Otherwise, anyone in the Internet can use your computer to back up their files without your knowledge. Never share any folder without a password.
Put a good password on your PC. If you have a password on your PC that is easy to guess, your computer can be easily taken over by hackers. A bad password would be things like 'password', '12345', your name, license plate number, or any word that could be found in an English dictionary or a dictionary in your native language.
Report any network slowness or strange computer behavior so it can be checked by me (if it's a network problem) or Brad (if it's a Windows or Mac problem).
Windows PCs with static IP numbers are especially easy targets. You should always set "Obtain an IP address automatically" in Windows unless you are running a server and you are knowledgeable in computer security.