Found this article from December on Microsoft's site, some pretty good readying, if you like this kind of stuff.
The Windows XP kernel includes a number of improvements over Windows 2000 that promote better scalability and overall performance. This article covers these changes and explains how they improve startup time, increase registry size limits, and promote more efficient disk partitioning. Windows XP provides support for 64-bit processors, which is covered here along with a discussion of how side-by-side assemblies end DLL Hell. Also new in the Windows XP kernel is a facility that will roll back driver installations to the Last Known Good state of the registry, making driver installation safer. Other topics include the new volume shadow copy facility, which provides for more accurate backups and improvements in remote debugging.
Although the number of changes to the Windows XP kernel is small compared to the changes between Windows NT 4.0 and Windows 2000 (the internal version number confirms this—Windows 2000 was originally Windows NT 5.0; Windows XP was version 5.1, not NT 6.0), there are a number of important changes that make Windows XP more reliable, more scalable, and more broadly compatible with existing applications. This article focuses on the kernel changes made to achieve these improvements. It does not cover many other user-mode enhancements in areas such as usability (improved shell and remote assistance), consumer features (CD burner support and DirectX 8.0), and other changes (terminal services with Windows XP Professional, fast user switching, and the new Windows XP Home Edition). Also, with the exception of System Restore, everything in this article applies to the upcoming Windows .NET Server family of products, since it will be based on the Windows XP kernel (with some additional features).

This is a nice read if you like it maybe you have done allready

http://msdn.microsoft.com/msdnmag/is...l/default.aspx