1) Click with right mouse button on the clock on your task bar. Choose "Adjust Date & Time". This opens a window on my RH8 box that allows you to specify the date, time and timezone. The same menu is reachable via
System settings -> Date & Time in my menu.
However, as you've indicated, the system queries a remote server to get the correct time. This is done via the NTP protocol. So, the ntp daemon, ntpd, is running and has been configured to get the date and time (not the timezone) from the remote servers.
If NTP is used, as on the server you talk about, then you shouldn't manually adjust the date and time. The NTP daemon will make sure the clock is right, in combination with the timezone you've set up.
2) Similarly, you can configure your Win boxes to query the date and time from an NTP server. However, it is considered as not-so-nice to the other internet people if all your boxes query the time from the worldwide NTP servers (who are used by many people), even though they are supposed to be able to handle such loads.
So, my advice is to simply set up your server as NTP server and make your Win boxes to be NTP clients who will query your server for it's time, rather than querying the remote servers.
So, basically you will have this setup:
remote -------> your server ------> your Win boxes
This will ensure that all clocks are correct.
To configure NTP clients for your Windows boxes, I recommend that you do some research on:
Windows Time service
and maybe also look for tips at http://jsifaq.com