Do not open any files attached to an email unless you know what it is, even if it appears to come from a dear friend or someone you know.
Some viruses can replicate themselves and spread through email.
Better be safe than sorry and confirm that they really sent it. Install a virus scanner on your computer. Update your scanners virus definitions every fifteen days. Back up your files on a regular basis. If a virus destroys your files, at least you can replace them with your back-up copy.