One curious thing about this is that it's a hybrid of source code and precompiled executable code.
You can find the bulk of the precompiled stuff in \base\ntos\build\prebuilt\i386\ntoswrk.lib - note that while the most of the other .lib files are just stubs to dlls, this contains actual object code. In fact, the .obj files are lined up inside it quite neatly and can be extracted using various tools.
For example, using IDA Pro you can quite easily analyse this file. This is the list of objects:
http://img375.imageshack.us/img375/9399/wrk1ik5.png and this is part of the kernel that frequently checks to see if you're fucking with the license data:
http://img375.imageshack.us/img375/5802/wrk2kg8.png - note the code to raise a SYSTEM_LICENSE_VIOLATION (0x9A) bluescreen when it sees foul play.
Of course, you can disassemble the retail kernels in a similar way, but it's nice to have it all laid out here with extra symbols, neatly packed away into objects that correspond directly to the original C/ASM source files. If you're into that sort of thing, anyway.