Google have recently updated their online 'docs viewer' to include online previews of many more formats (see: http://gmailblog.blogspot.com/2011/02/12-new-file-formats-in-google-docs.html) it's possible to put files through the viewer by using the following url: http://docs.google.com/viewer?url=<<url of file>>.

Adding an option in the 'display option' drop down may be a way of ensuring consistency of file access that is not dependent on what software is installed or which OS the user is on.