A warning to beware of a virus that can be spread by email is usually the sign of a hoax (such as with the infamous "Good Times" virus, as explained more in a web page describing email virus hoaxes). However, PC Week reports on a Word macro virus that can indeed by spread by email with Microsoft Mail on a PC.
Update: The virus is called the ShareFun.A virus and is described more on an McAfee web page. Technically, it does not spread just by reading the email message. You have to open the attached document to get infected. What's new here is that this virus will actually initiate an action to send copies of infected documents to other randomly selected users on your Mail mail list. They will receive a message with a subject that says, "You have GOT to read this!"