A nice tip from Linux Screw on converting .NRG files to .ISO files.
"In case you need to convert Nero image file .nrg into regular ISO9660 .iso utility nrg2iso might be helpful then. Its included into apt repositories of Debian and Ubuntu, so to install it execute:"
sudo aptitude install nrg2iso
When its done, convert file by command:
nrg2iso image.nrg image.iso
---Convert Nero image (.nrg) to ISO9660 (.iso) | Linux Screw