Hi JCH,
I recently bought a 2001 (Y) DHSE with sat nav.it came with a genuinedisc from land rover dated 2001. i managed to find an update on ebay. its a 2003 disc and its made by Navteq. the roads are a bit more up to date and it has more local information (petrol stations etc) listed. i paid about £50 for the disc on ebay. i think you can also buy them new from LR - £130
Will