@W3bbo:

No it doesn't, and Windows itself has never supported vertical UI layout.

Michael Kaplan's blog is a good resource on this:

http://blogs.msdn.com/b/michkap/archive/2010/09/22/10066037.aspx

And he has a quote from someone in the WPF dev team:

It was decided not to support vertical layout for East Asian text in the initial release of WPF as part of setting a reasonable limit to the scope for that release. It is a recognized gap that is being considered for a future version.

That was in 2007, and its still not there as far as I can figure out. Notice that there's a RightToLeft property on controls, but no vertical formatting property.