Sorry Kate but it's a bug bear with the JDM sat nav. Their is a company which does a conversion but they take most of the old stuff outand can cost up to £900. You'll also find that the radio frequency range is different and you'll not be able all the radio stations.
You'll need one of these to sort that out.
http://www.funkystyling.co.uk/item_deta ... prodID=369
if you ask chris nicely at funkystyling he may do you a bit of discount.