The Americans have a permanent problem. They can never agree on standards that the world has accepted, and always want to be different. Be it starting baseball and not playing cricket or having their own set or measures in Oz and the most irritating method of writing dates MM/DD/YY
Thus after the perennial struggle with mm/dd/yy format , i finally decided to rid my win-box of this malaise, once and for all.
So if u folks want to change the default date format to dd/mm/yy or dd/mm/yyyy try this
Goto Control Panel(Classic)/Regional and Language options
Then choose English (uk) or in English (us), click on Customise and then goto Date and make changes so that the default date will be in format dd/mm/yy, in short date and dd/mm/yyyy in the long one or whatever u prefer.While ur at it u can even change the currency and do a whole lot of other things. Remember to save and close. This also comes in handy even when u want to change language.