AFAIK the XBox and WMP are UPnP AV Clients, and don't use DPWS. Vista includes WMC (Windows Media Connect) which also uses UPnP AV to serve Media. I believe UPnP AV also underlies the DLNA spec for compatibility between media sharing devices.
There is an unmanaged DPWS stack (WSDAPI) included in Vista, but I think it is used/meant for communication with more resource constrained devices like printers, scanners and home automation. There's also a corresponding WSDAPI stack in the .Net Micro Framework. It looks like it's intended to be used in concert with the Windows Rally family of protocols.
PS: TMA