If you have an Xbox 360 HD DVD player, you'll be prompted for an auto update the next time you watch an HD DVD movie (and your are signed into Xbox Live.)
This update includes:
* Compatibility improvements with certain titles
* Additional support for network features
If you don't have access to Xbox Live, this update will be available for download from Xbox.com later this week.
I cannot help but wonder what these network features are, or why Microsoft would release this now...