Read original post by Jared Bienz at The Good, The Bad and The Mobile
In this article I want to expand on the information already available about porting user interfaces from Windows Phone to Windows 8. The most important place to start is an article titled Porting Silverlight or WPF XAML/code to a Metro style app on MSDN. It covers slight changes in the Application object, Window object and Navigation system. It also covers more involved changes to the Resource model and to Touch. I’ll talk briefly about touch at the end of this post and I’m dedicating an entire article to resources (hyperlink here when it’s done). If you haven’t done so yet, consider switching over to the official guide and coming back here when you’re done.