(DST) Meeting requests between companies/time zones off by 1 hour

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I have a brand new Exchange 2003 SP2 install with all windows updates.
All internal calendar appointments are the correct time, and repeating
appointments adjusted to the new DST settings correctly.

We've had three companies not in our same time zone whose meeting
requests show up an hour off.
I can't find any way to tell just by looking at the messages whose
system is the one that has the incorrect settings.

.