NTP or Network time protocol is a means of disseminating time around a network. SNTP or simple network time protocol utilises the same protocol as NTP but is missing the complex filtering algorithms to maintain an accurate time.
SNTP is usually used on the 'leaves' of a network to synchronise workstations where the accuracy of NTP is not required.
NTP is mainly distubuted as a LINUX \ UNIX daemon, however, it does have a port to Windows NT. Windows 2000 and XP have a SNTP client supplied with the operating system which does not have the filtering complexities of true NTP.