From the viewpoint of copyright protection, it is also possible that Windows Vista will not be able to play next-generation DVDs

Even if you attempt to play Blu - ray or HD - DVD video software on a PC, the signal will not be output if the video card and monitor you are using do not support copyright protection technology. This is because Microsoft received a strong request from Hollywood because it implemented the function in the next OS "Windows Vista".

What is this all about?

Details are as follows.
High-quality DVDs will not operate on some Vista PCs - Industry sectors - Times Online

According to this article, when transmitting a video signal from a PC to a monitor connected digitally with a conventional monitor, we received a strong request from Hollywood because there is a possibility to capture the signal and make copies Microsoft said that Windows Vista installed a function to prevent video signals from being output when next-generation DVDs were played back by connecting a video card that supports digital connections and a monitor.

Incidentally, a monitor that supports copyright protection technology "High-bandwidth Digital Content Protection (HDCP)" that prevents illegal copying of contents by encrypting the video signal transmitted from the PC to the monitor If it is, it is possible to reproduce the next generation DVD.

For the copy guard, the following links are detailed.

Copy guard - Wikipedia

Moreover, it seems that backup software has already been developed for HD-DVD.

BackupHDDVD, a tool to decrypt AACS protected movies - Page 13 - Doom 9's Forum

Additional notes
Although it seems that Windows XP can not be viewed even if you connect the video card and monitor which are not compatible with HDCP by digital connection, it seems that Windows Vista does not output signals at the OS level. In other words, it seems that it began to prevent illegal copy at the time of OS as well as video card and monitor.