Win8 development is only supported on Win8. VS installs on any Windows OS from Vista onwards to support classic app development, but as you see you won’t have access to the Win8 app styles.
Since Win8 rc is available for free, you can download it and install it on a virtual machine and code on that for a low cost workaround. You don’t need to have it be your primary OS. Developing in a VM has a ton of benefits.