If you are on a domain DON'T use 3rd party time-sync's !!!!
The domain will take care of it and it better be the only one that handles time-sync for the Windows boxes.
(Domain computers need to be on the same (or very close) clocks in order for authentication to work properly.)
Non-Domain Windows PC's can be set to use the domain controller as time-source (each DC acts as SNTP time-server automatically).
3rd party of MS own doesn't really matter. As of XP/W2K3 the MS time-sync works just fine. It's just a bit basic, but good enough.
Bear in mind that for any NTP or SNTP based time-sync you need access to the time-servers.
By default this is usually "time.windows.com" (Microsoft) or "ntp.pool.org" (anything else) on the internet. If the company firewall doesn't allow this you will have to use an internal time-source and configure the software accordingly.
If you are not sure if there is an internal time-source available go talk to the network administrators. They need one too and usually have a good time-infrastructure ready for use.