I had always disabled the windows time service because I didn't see any obvious way to configure it and I was frankly too lazy to go find how to do it; however, on a couple of systems the time was very important and I was required to get it working.
Courtesy of www.regedit.com:
Start -> Run -> RegEdt32
Delete value Period
Add Value: Period (REG_DWORD)
0 - once a day
65535 - once every 2 days
65534 - once every 3 days
65533 - once every week (7 days)
65532 - once every 45 minutes until 3 good synchronizations occur, then once every 8 hours (3 per day) [default]
65531 - once every 45 minutes until 1 good synchronization occurs, then once every day
Change Value: Type
Set to 'NTP' (It is probably NT5DS)
Add Value: NtpServer (REG_SZ)
Set to 'Your_timeserver_here'
Add Value: ReliableTimeSource (REG_DWORD)
Set to '0'
Control Panel->administrative tools->services
(you might have to enable it if you disabled)