AFAIK there is NO free viewer, there is
Steelray and
projectviewer, each costing around $30.
Micrososfts "official" POV is that Project lets you save the files as HTML, so your clients can view them on the web... Which of course is kind of bogus....
If you have files smaller than 400k, then try the projectviewer demo:
http://www.projectviewercentral.com/...ewer/demo.html