MonthCalendar width on different (platforms), correction: themes (XP vs Aero theme)

Apparently the .NET monthcalendar renders differently on different platforms. A calendar on Vista is wider than a XP calendar.

I want to make the calendar fit nicely and precise on all platforms. Is there a way to do this, without having to measure and hard code the different widths ?

..............

Edit/Correction : The calendar seems to render differently based on the theme you select :

How to compensate for that ?