I've been starting to hack on Windows 8 a bit, using C# and XAML and the .NET 4.5 Framework. Y'all will probably figure this out, but if you don't, here's the deal: when you go to add references to system libraries, none of your favorites (System.Web, System.Net, System.Security, PresentationCore, etc.) will show up. You have to manually browse to C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5 and walla, there they all are in their .NET glory. Party on.
Or not. Didn’t realize this could get you in trouble when you go to submit. Look here for the libraries available to you: http://msdn.microsoft.com/en-us/library/windows/apps/br230232%28v=VS.85%29.aspx
Beware though: .NET in Windows 8 is not exactly .NET. This reference page starts to explain http://msdn.microsoft.com/en-us/library/windows/apps/br230302(v=VS.85).aspx and this presentation http://channel9.msdn.com/Events/BUILD/BUILD2011/TOOL-930C by the eminent Krzysztof Cwalina definitely helps.