Make a backup first as I've only just worked this out and it may have flaws!!!!!
Open up jquery-ui1.7.1.custom.min.js which is inside the CSSFormBuilder/Datepicker folder somewhere
Find dateFormat:"mm/dd/yy" change it to dateFormat:"dd/mm/yy"
Then on the page where you have your form find
var Date_group_Best_day_Spry = new Spry.Widget.ValidationTextField("Date_group_Best_day_Spry", "date", { format:'mm/dd/yyyy' , validateOn:["blur"]});
and change that date format as well so that the validation works.
I tried a test form and it worked for me. I haven't tried entering it into a database or sending the form.
Good luck.