I've been doing a lot of research on how to do this as I am from Manila, Philippines and I imported my Z from the US so it comes with the US map. I'm desperately trying in vain to update the map specific to me to no avail.
From what I gathered, you can order update DVD's for Europe from
NAVTEQ Maps and Traffic. They will sell you the update DVD specific for 370Z's. Navteq is the company that created the GIS map for the 370Z.
Unfortunately they do not have an update for me.