The article is on slashdot too, if you can't get on the neowin site.
If is very unlikely that the full source code has been released, since the file in question uncompresses to about a full cd, and the full win2k source code is about 40 gigs I believe. Also, no single person has access to the full source code, for this very reason.
Depending on what is included, assuming that this is real, it could help windows on xbox, and wine development...except for the fact that developers won't even look at the source code, for fear that their work will be tainted, and MS layers will rain down upon them.
Too bad they didn't leak the private RSA key xbes are signed with...