Place the following in the login script, start up folder, and/or schedule it: (This works on NT and 95)

NET TIME \\ServerName /SET /YES

You can configure the PDC or BDC to be the default time server by editing the registry at:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters

and adding a Value Name of timesource as type REG_DWORD and setting it to 1. Stop and restart the server service for this change to take effect.

For WinNT users, you must grant the user the right to change the system time or use TIMESERV from the reskit.