Control Panel->Regional Options controls how this is displayed in Outlook.

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Milly Staples [MVP - Outlook]
Post all replies to the group to keep the discussion intact. Due to
the (insert latest virus name here) virus, all mail sent to my personal
account will be deleted without reading.
After furious head scratching, Perscon asked:
| How do you change the month above each calendar (ie "05" instead of
| "May") ? My small calendars are showing "05 2005" instead of the
| original "May 2005".