Disk Versions for SatNav?

My in-laws have a 2003 Discovery. It has the single-DIN Nav system, but he didn't get a disk with it.

Looking online (eBay etc) there are loads of different disks, but I'd like to know which will work.

I imagine a more recent map version than the disco 2 will probably not work on that old system? What's the newest ma that will work?

Thanks

What's the satnav system? VDO Dayton with a CD-rom unit under the passenger seat?

navteq discs might work.

EDIT - check out my thread for the above system in my 2001 D2 http://www.landyzone.co.uk/lz/f8/vdo-dayton-ms3100-satnav-works-d-227922.html

OK, I saw the in-laws today and had a look at the system.
It seems he did have a disk with the car, it was the unit itself giving him problems! He'd like to know if he can get it working, I guess then there is still the question of any updated disks from later years that could work.

The headunit is called Navisys. It takes the Navigation CD in the headunit (Does this mean you can't listen to a CD while using the satnav? Or does it keep the route in memory?)
Under the passenger seat is what looks like an amp - It's labelled Harman Kardon H70858.

We tried the unit again, and it does accept the 2003 disk he got with the vehicle, but doesn't ever find a signal.
Before starting nav the screen displays 'GPS Antenna Error'. When you put the disk in and a destination is found, all looks OK, but 'Calc Route' stays on screen forever. There's no error message as such.

So I guess there's a problem with the antenna. Is it likely to be the antenna itself, a connection (to the back of the headunit?) or the main headunit?

Thanks

I think you've probably got a CD changer underneath the driver's seat for playing music.

David

I had a good look under the passenger seat, even photographed the amp - I didn't even think to look under the driver's seat!! Yes that would make sense re: the changer!

My 2004 has the sat nav it's not that good and yes it takes an age to calculate the route