You can just go straight to the latest OS release disk-- V28.

It is good to get the current map disk too, but not critical. I assume that your car probably has a 2002 map DVD. That will work fine with the latest OS, but it is nice to get the latest roads and POI database.

__________________
SOLD
2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input