check out ebay....this is the guy I use..and he is reliable
he will upgarde the firmware and the maps for a lot less than BMW. You will also get 3D maps as standard as well.
eBay.co.uk: BMW SAT NAV V27 + V27.1 + V28 OPERATING SYSTEM UPGRADE (item 120091641935 end time 08-Mar-07 14:03:59 GMT)