From the release:
When you use the Xbox 360 Wireless or Wired Headset with the Xbox 360 Wireless Receiver for Windows or the Xbox 360 Wireless Controller for Windows, it will be recognized as a second sound device. That means you can configure the headset in games that use voice communication or voice over IP programs.
For example, in Games for Windows title, Flight Simulator X, you can output voice communication and radio chatter through the Xbox 360 Wireless or Wired Headset, while still hearing the airplane noise through your main speakers just like a real cockpit!
Talk to other gamers through the Xbox 360 Wireless Headset when you play online via Games for Windows - Live, soon to hit Windows Vista with Shadowrun, UNO and Halo 2 for Windows Vista, later this year. Use the Xbox 360 Wireless Headset to chat with friends online on MSN Messenger and other applications that use a voice input device.
Use the Xbox 360 Wireless Controller for Windows with all of Windows Vistas inbox games or navigate Windows Media Center.