My 2001 XS has a vdo dayton install: The main unit is under the passenger seat, the gps antenna and the loudspeaker are in the instrument binnacle.Screen is mounted just in front of transfer box lever.
Anyhow - my point is, an ebay search revealed a current update CD for about £17 for the system. If yours uses a CD then gpsunderground as Ste said, and ebay may be able to sort it. OK, in my case there's no fancy 3d screen or postcode input, but it certainly works.