They are correct in that .nrg is an Image format for Nero. What you need to do is either convert it to the .iso format so you can use pretty much any burning program to burn it, or get Nero to burn it.
Now, by burning it, I don't mean put the .nrg/.iso file on the disk like it is a file, but to use the "Burn image file" option in your burner application to OPEN the file and create the disc that way.
Also, if you convert it to .iso format, there are tons of programs out there that will allow you to open, extract or mount the file so you can see inside of it and use it as you want.
From there, you'll have to do your video conversion or whatever.