Thanks for the response, but it didn't work out in that way. My Blu-ray player has rejected the created CD-R with an error message.
First, I should mention that the firmware upgrade file has the extension .FRM, so I assume it wouldn't be recognised by ImgBurn anyway.
When I loaded a blank CD-R, I first had to choose between two formatting options:
Like a USB flash drive (Live File System)
To use with a CD/DVD player (Mastered)
I chose "Mastered" but I'm not sure if this is correct. It then prompted me to select the file(s) to be burned to the CD-R, and this appeared to be done entirely via Windows Explorer. ImgBurn was not launched.
I know that Windows Vista has no native support for the ISO9660 format, but I'm not sure whether this is also the case in Windows 7. If it is, then I imagine I would have to use a proprietory disc burner.
Obviously I need some further guidance on all this. Anyone?
Edit: I've now successfully used ImgBurn to create the CD-R. (I've now hit a problem with the upgrade in the Blu-ray player, but that's for a different forum!) Anyway, thanks for the help.