Changing Timeserver via a REG Script

Hi,

Actually I would like to do this on Windows XP Pro. I
have a network of PCs across a WAN. I would like to put a
server at each location to do specfic server duties. 2 of
the duties being a timeserver and another being a spot to
pull down Windows updates.
I know that I can go into Group Policys on the local box
and make these changes, but instead of doing that for each
PC cause each location will have its on server.
How would I write a reg script to point to a unique server
for pulling down time and Windows updates?

Thanks,

Tony P.S. This is on a Windows NT 4.0 domain, so no
Active Directory (yet)