As far as I know, it won't be possible for you to do this. Even if you manage to do this somehow, you will face a lot of issues. The reason being the fact that Windows operating system is a very resource intensive application and if you run a Windows VPS inside a Linux VPS, it won't work properly. Therefore, it's recommended that you don't try.
it might be possible, but i highly recommend against it
your "outer" xen vps is exposed to the VT-x ( virtualization ) execution instructions of the processor, but the "inner" one won't be... therefore, it'll be slow