To get started, install Apple's Bonjour for Windows and Pleasance's client on your Media Center PC. From there, fire up your iPhone or iPad and send over some photos or movies (note that music isn't supported yet).
The Digital Lifestyle has posted a hands-on with the setup, noting, "I was impressed how quickly video playback started, within seconds of selecting Windows Media Center Airplay option my Media Center PC was playing the video and without leaving Media Center at all."
Sounds good! Let us know how this goes if you try it out.