If you get a document sent to you from someone who created it using an Office 2007 program, you won't be able to open in older versions of Office unless they saved it that way. If you get an error when you try to open a document like this, Microsoft does offer a free conversion program (link below) that allows you to convert an Office 2007 document so that it can be opened by older versions of Office programs. While you may lose some 2007-specific feature functionality, you'll at least be able to see the content of the document.