What OS is required to play a WMV-HD title?
Windows XP is the preferred OS for WMV-HD playback. There are many reasons for this, the top one being only WMP 9 for XP allows for WMA Pro 5.1 decoding. So if you wish to enjoy the 5.1 sound track you must have Windows XP with WMP 9. Windows 98SE/ME/2000 may be used as long as you have Windows Media Player 9 installed. The 5.1 channel WMA Pro will be down-mixed to 2 channel stereo when using Windows 98SE/ME/2000.