Outlook 2K resets labor day hours

I have two client machines, running Win98 & Outlook 2K, that behavior in a particular manner, related to calendar hours:
a) If you set up a date using the form, and de begin an end hour is AM, the form reset itself to the same hour, but PM. The only way to program the date correctly is by drag-and-drop.
2) If you try to change the standard begin-end hours of the tipical labor day (Tools/options), the same problem occur: the form reset itself to PM the begin hour, as soon as you change the focus from this control.
The server runs NT SP6 and Exchange 3.3

Any idea of what?s wrong?