Hi Doug--thanks so much for drawing this to my attention. When the sample was updated the name of the final .msi changed, but I didn't notice that when I updated the Downloads page.
The correct path is this:
http://download.microsoft.com/download/B/9/8/B982BFD9-3E17-426A-A537-833BEF376698/MGrammarXAML.msiwhich I have verified. I've changed the XML file that makes up the downloads page, so that should appear correctly soon.
.Kraig