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.
. If someone can't manage to get it installed and working, they have no business using bitcoin.
We should not write our own buggy implementation of NTP when other good options exist. Notice that bitcoin does not include an antivirus scanner either, but the same arguments that would apply to including NTP would also apply equally well to virus protection.