Ars Technica has more on Windows 7 core and MinWin kernel. Here's a bit:

Why "Windows 7"? The number is based on Microsoft's internal operating system numbers: the first version of Windows NT, 3.1, was given the same number as the "Classic" Windows when it was released in 1992. Since then there has been NT 4, Windows 2000 (NT 5), Windows XP (NT 5.1), and Windows Vista (NT 6). You can check these numbers by typing "ver" at a command prompt on any of these operating systems.

Traut ran a stripped-down version of Windows 7 called "MinWin" that included only the core kernel: for the first time Windows NT has been seen running naked, without even a GUI to dress itself. It ran only a miniature web server that would display simple HTML pages, including some dynamically-generated pages that showed the task list and other properties of MinWin itself. Thirteen tasks were running, most of which would be familiar to anyone who has opened Task Manager: smss.exe, csrss.exe, and svchost.exe were all there, plus the mini web server httpsrv.exe. The OS ran under Virtual PC, and this allowed Traut to show the audience exactly how many resources it was consuming: about 25MB on disk (compare with 14GB for a full Vista install) and 40MB of RAM. The OS booted up in about 20 seconds inside Virtual PC. Still not quite as lightweight as, say, AmigaOS or QNX, but remarkably small for Windows. Traut admitted that he would "still like to see it get smaller."