i know but doesn't work like that, nero doesn't recognize them as image files

latest nero? you didn't forget to UNZIP it?

yes very recent nero, and yes I unzipt it, and i got an iso file then and an img file

I've written Koppix today (Linux) and it was a .iso (KNOPPIX_V3.2-2003-06-06-EN.iso)

just burn the .iso with nero (file>burn image)

If nero won't show the image, just select show all files and select it anyway.
It will burn it.