In Windows 7:
Set Time and Date (Windows Clock, Right click)
[Shield Icon]Change Time and Date
Calender Settings
2 Windows Pop up (for me)in one you can change your seperator in the "Numbers" tab
in the other window you can change (in the "Formats" tab) your "Date (Long)" Format to a shorter one so it gets correclty drawn
some info might be incorrect, i translated it freely from my german install