I agree with the sentiment of others and would stay away from bmwnav.net as it just doesn't feel right.
You can save a little money on the latest map DVD if you order it from a dealer like Tischer BMW (
http://getbmwparts.com). They have it at $169.15 instead of the retail $199. The part number for the 2009.1 NA maps for the Z4 is 65 90 2 147 669.