Yes that's where I'm at. The Jap update disk has the boot code I need to create the hybrid upgrade disk that will make your sat nav UK spec.
In other news I converted a TomTom 520 to a 530 the other day using some hacked update code and I'm thinking this is the replacement unit of choice for the 350Z. It has @*!# hot satnav (with lane guidance etc), mp3 playback, line out, phone integration etc etc. And I think it can be made to fit nicely in the gap where the 350Z sat nav screen lives.