If you do not use Microsoft Office 2007 or higher (2010 was just released in beta) and receive a document from an OLT staff member who does, you can still view the file after following the link below to download Microsoft's compatibility pack.
http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=941b3470-3ae9-4aee-8f43-c6bb74cd1466