Thanks Tony and Ben
As I stated, I tried with 3 PCs and 3 DVD-RW's - the latest being only
a recent purchasre - an Asus SATA DVD-RW.
Anyway, managed to burn the .iso to a dual/double-layer DVD+R with
Brasero under XUbuntu 9.04.
at (near) completion I got an error message, but I can play the full
movie and extras using SMPlayer, so I'm not sure what problem was but
I think that it was something to do with creating a new checksum.
When I have time I'll investigate further.
With Mint7 on 2 of the PCs I got the message (using Brasero) "medium
is not writeable with current set of plugins" though as stated I can
play the written DVD on one of these PCs with SMPLayer and Kubuntu 8.04.