Yes, Windows 8 does support DirectX 9.
For development, the old DirectX SDK is now deprecated, but you'll have all the libraries and headers you need within the new Windows 8 SDK, which comes included with Visual Studio 2012. You can go for the "old way" with no problem. If you need PIX for some debugging, or the high level D3DX library, you'll have to install the old DXSDK again, as this is not in the Windows 8 SDK.
However this is only valid for plain old desktop apps. For Metro-style apps, I'll let Chuck Walbourn from Microsoft speak:
Direct3D9 and Direct3D9Ex are not supported for Metro style
applications. Use of the DirectX SDK with Metro style applications is
not recommended or supported. See
http://msdn.microsoft.com/en-us/library/ee663275.aspx.
There are a number of resources available to help you in porting a
Direct3D 9 codebase to Direct3D 11. The majority of the material for
porting from Direct3D 9 to Direct3D 10.x applies fully here since
Direct3D 11's API is very similiar to Direct3D 10.
See
http://blogs.msdn.com/b/chuckw/archive/2011/07/11/getting-started-with-direct3d-11.aspx.
Be sure to review the Windows to Reality: Getting the Most out of
Direct3D 10 Graphics in Your Games presentation as it covers numerous
pitfalls and performance issues developers have hit in the past, and
DirectX 11 Technology Update for a summary of the differences between
Direct3D 10.x and Direct3D 11.
MSDN has a porting guide as well
http://msdn.microsoft.com/en-us/library/ff476190.aspx which points you
to http://msdn.microsoft.com/en-us/library/bb205073.aspx for going
directly from Direct3D 9 to Direct3D 11.
Sorry, you can't use D3D9 directly for Metro-style apps. But you can use D3D11 and limit yourself to some feature level (e.g. D3D_FEATURE_LEVEL_9_3) if you want to support legacy hardware.
