NeroLINUX is not able to convert any movie file to DVD Video. It let you burn a DVD Video following the spec when you already have the .vob files.
If your Nero came with your burner, you normally have an OEM version. In that case, the serial number will not work with NeroLINUX. You can buy a standalone NeroLINUX sn on http://www.nero.com/eng/catalog.html