Date Format Problem

I've been running webwiz for a few weeks now and our users love it. Their only gripe is the default date format. Us silly americans have grown use to the mm/dd/yyyy format.  I set this as the default in the admin panel, but it still defaults to dd/mm/yyyy. If the user sets their own preference in the member control panel it works fine, but

If you change the default date to mm/dd/yyyy format in the admin area this will not change it for users who are already registered as they would need to choose their own date format from their forum profile.

It will change the default date to mm/dd/yyyy for those people not logged in and for new signups who's default date settings would be set to that in the admin area unless they override them by setting their own date format.

It could be because of that as new users are created differently when using AD