BIOS passwords offer absolutely no protection against viruses. Its just there to slow people down who are trying to use your computer without your permission. Most computers have a "bios password ignore" or "bios password reset" jumper somewhere so its not even that secure. Might slow someone down maybe 5 minutes.
The blanket recommendation is to get a good antivirus program and let it hog your cpu in the background. That's not what I do. The problem with antivirus programs is that they are generally no good for viruses that are not in their database. Likewise, when a new one comes out, several thousand people usually get infected until the antivirus people can update their database. Then don't get me started on mutating viruses.
The simplest thing to make it really hard for viruses to infect your computer is to create a user with limited privileges and use that, rather than admin. That way, if you get tricked into loading a virus, it doesn't have enough system privilege to do any real harm. Just don't let them con you into entering the admin password when you weren't really doing anything that would call for it.