Try this code in a Workspace:
|aDate bDate|
Transcript open.
aDate := Date fromString: '02.25.2011'.
Transcript cr; show: aDate; cr.
bDate := aDate subtractDays: 734503.
Transcript show: bDate; cr; show: 'Year zero! Which calendar does Pharo officially use?'.
From
http://en.wikipedia.org/wiki/0_(year):"Year zero" does not exist in the widely used Gregorian calendar or in its predecessor, the Julian calendar. Under those systems, the year 1 BC is followed by AD 1. However, there is a year zero in astronomical year numbering (where it coincides with the Julian year 1 BC) and in ISO 8601:2004 (where it coincides with the Gregorian year 1 BC) as well as in all Buddhist and Hindu calendars.