This is huge. Having this running inside your Windows 7 installation will ensure compatibility with older programs while still being able to benefit from the performance, stability and security advances of Windows 7. This is a glimpse into the future of Windows installations.

Secret No More: Revealing Windows XP Mode for Windows 7 - SuperSite Blog

This is good news to be sure. The Beta was stunningly good, but the lack of drivers really hampered my daily usage of it. I am looking forward to this nearly-complete version solving most of those issues and smoothing out some of the rough edges. There still are those pesky rumors of a separate version of Windows 7 being developed simultaneous to this one that has a modified UI. Not sure I am real thrilled with that prospect, but we shall see.

http://blogs.zdnet.com/microsoft/?p=2547