I've put a support call in to Business Objects regarding this issue and i can honistely say they are crap, it looks like they only want to support Americanised dates.
1st Try setting all the dates via the custom mode, this should work except for the tree view.
My support call rose around the inconsitency in the data viewed in the tree.
2nd Look at HKEY_USERS\.DEFAULT\Control Panel\International\shortDate
key to the specific format
add RDC component (CRAXDRT.DLL) into a COM+ package and make it run under a User account.