It's ok that you have 2010 installed. From the SDK download page, "The Windows Phone SDK provides a stand-alone Visual Studio Express 2012 edition for Windows Phone"
The bug you are running into is a known issue for x64 systems and one I ran into myself even with VS 2012 installed. I wrote about it in a [blog post a few days ago] and the solution is described in KB2897627.
Note: they've actually updated the KB in recent days; the solution used to be a bit more involved.