Antivirus software is the answer.  There are several free programs (AVG and Avast are two examples) that can help protect you from viruses.  Keep them up-to-date, and you should have no worries.  MACs are the target of viruses as well, though admitedly fewer than Windows systems.\n\nAlso, be a "safe surfer"--don't visit websites of questionable reputation, and don't open every attachment your friends send you, as it may have been a virus that sent it in the first place!
Switch to Mac?