With regards to the suggestions of integrating NTP into the bitcoin client, I think it is a bad idea. The bitcoin client is simply not an appropriate place to put timekeeping software.
Probably correct.
I'm going to side with ArtForz and his idea of built-in SNTP for the Windows version of bitcoin. The native Windows NTP works well only in domains. For the regular Windows boxes that are just members of a workgroup there are multiple problems. Majority of those problems are caused by the various add-ons, but I don't know how many people run just bare Windows machines with software only from Microsoft.
The code to properly query the Windows Time Service would be more complex than just a simplest generic SNTP code.