I receive several virus emails a week.
1) Keeping your anit-virus up-to-date is well worth it.
2) If you are on any version of Microsoft Windows, it is advisable to periodically go to windowsupdate.microsoft.com and install any security or critical updates shown.
3) If you get one of these, don't be too quick to blame the person shown in the "from" line. Many of these viruses, once they infect a computer, will use "spoofing" when they spread. The virus will send emails to individuals in the Address Book and will insert another name from the Address Book into the "from" line, making it look like the message is coming from a different computer than it actually is.