The March issue of TechNet Magazine offers in-depth coverage about many aspects of the new Windows Server 2008.
Since Windows Server 2008 has the same kernel as Windows Vista SP1, Windows Server 2008 includes many of the enhancements Mark already discussed in three part series, "Inside the Windows Vista Kernel." So you may want to check out those three articles, as well (Part 1, Part 2, Part 3).
In his article "Inside Windows Server 2008 Kernel Changes," Mark Russinovich details many changes to the kernel that will effect server performance. He explains how Windows Server 2008 improves stability, offers a mor scalable environment, improves performance, delivers powerful virtualization capabilities, and more.