I've been trying this for a while, just using the free version of Xamarin. Here's where I am so far:
I have a published Windows Store app (just build on the default Windows Store library)
I have managed to get this into Xamarin studio, basically by hacking the csproj file
My current problem is that I'm getting build errors because it's missing references. There does appear to be some equivalent Mono / .Net4 libraries, but it feels like I'm going about this the wrong way. Is there a single reference, or way to bring across the Windows Store API reference?