The time would not stay synchronized on my Windows 7 machine. It looked like it was configured to sync with DC3, but it was not working. After some research I found a hotfix, http://support.microsoft.com/kb/978714, that fixed it. I used this command to configure the time synchronization:
w32tm /config /manualpeerlist:time-a.timefreq.bldrdoc.gov /update /syncfromflags:manual
See http://support.microsoft.com/kb/223184 for additional settings in the registry. This KB article is for Windows 2000. I could not find a KB article for Windows 7, but I think most of these settings still work. There are other documents from Microsoft about this, but I just liked this KB article best.