DO NOT OPEN THE ATTACHMENT!!
It sounds like a classic attempt to send you a virus. If the accompanying e-mail isn't from anyone you recognise, $hitcan the whole message. If the accompanying e-mail is from someone you do know, don't open the attachment, just e-mail them to ask whether they've sent you any attachments...
I really wish that someone would catch one of these Spam-sending $hits and then boil them alive in their own excrement.....