It's definitely CDs I'm trying, not DVDs.
I do know why you asked though Matt, as I've come across so many people on various forums asking if the DVD version will work in their car's CD drive etc!
New Update for Ian, Matt and others:
I've tried a legit 2004 Carminat CD and it was accepted by my drive, which now shows the M6 Toll, whereas my 2003 map CD didn't show the M6 Toll.
It did not accept a copy of the 2004 CD though, which I made our of paranoia, in case the drive ate/damaged my legit 2004 CD. At least the drive accepted the 2004 legit CD though, which is a start.
So maybe it's not the drive?
It's still not accepting any languages CDs (all legit) and it's still rejecting the 2008 map CD though?!
To be honest, as it's a CD-based system, I don't really expect it to be able to take 2008, 9, 10 etc, but if I can get it updated as far as possible, I'd be well happy. So I've stepped up from 2003 to 2004 as a start.
Any idea if the V26 CD will work, giving me 2006 or 2007 maps?