Since Tracy wondered:

<<(aside from the obvious, Judaism, I think they start the week on sunset of
Friday) >>

1. In Jewish practice, the day begins and ends at sunset, probably based on
the first chapter of Genesis ("And it was evening and it was morning on the
nth day.")

2. The Sabbath (from Heb. "Shabbat") is the seventh day of the week.  It
starts at sunset on Friday (well, 18 minutes before sunset. I mention this
technicality lest someone "correct" me).  It ends at sunset on Saturday (well,
variously 30-40 minutes after sunset.  I mention this...)

3. Thus the first day of the week begins on what we think of as Saturday
night.

4. This has nothing to do with CALENDAR.PUB.SYS (I read that it will be part
of 6.0).

Leonard Berkowitz