thanks for posting this Jon, I've been suffering with this problem for ages, emailed TomTom support and various folk with no luck!
Just off to try it out now
I hope you don't mind if I post a link from my website back to this page to help others out.
For the guy asking about what regeditor to use, I used PHM
http://www.phm.lu/Products/PocketPC/RegEdit/
Regards,
Greg