Save the file first - then right click on it - and choose Open With - then choose MSWord to open it with. At that point, if you do have MSWord, you can set this to be the standard program to open doc files.
If you don't have Word try Wordpad. Otherwise download the free MSWord viewer and install it - then the attachment should open.
If you have Word, but the document is trying to open with Adobe Rader - then changing the program as per the earlier paragraph should work for the future too.