normanS wrote:

How often does Windows XP update the system clock from RTC?

AFAIK, WinXP doesn't ever update the system clock from the RTC. If you have a Windows domain server, the WinXP boxes may very well be synchronized to that (I don't know the frequency or accuracy). If you have enabled Internet Time and set a server to get time from (it defaults to time.windows.com), then it will sync to that time source once a week. If you need to have the time synchronized between the machines on your network, and you also want it synchronized accurately, you can use NTP. It's really not very difficult to set up and administer under any Linux (though by the volumes of documentation for it would make seem that it is). An alternative for Windows is Automachron (http://oneguycoding.com/). It supports both the TIME protocol and various versions of SNTP, with configurable synchronization intervals. On my network, I have one Linux box that syncs to external NTP servers, and everything else syncs to it (other Linux and Solaris boxes via NTP and WinXP boxes via Automachron).