I found the following guide on the Ubuntu forums (see below for a link). It should work from most linux distros:
Make a directory to hold the contents of the UNR DVD image:
$ mkdir unr
Make a mount point to mount the UNR .img file:
$ mkdir realunr
Mount the UNR .img as a loop device:
$ sudo mount -o loop -t vfat ubuntu-9.04-netbook-remix-i386.img realunr/
Copy all the contents from the UNR image to your unr/ directory. Note that realunr/.diskimage is critical:
$ rsync -a realunr/ unr/
Rename syslinux to isolinux:
unr$ mv syslinux isolinux
unr$ mv isolinux/syslinux.cfg isolinux/isolinux.cfg
Generate a DVD image from the contens of unr with the following incantation:
mkisofs -o ubuntu-9.04-netbook-remix-i386.iso -r -J -l \
-V "Ubuntu-Netbook-Remix 9.04 i386" -b isolinux/isolinux.bin \
-c isolinux/boot.cat -no-emul-boot -boot-load-size 4 \
-boot-info-table unr/
mkisofs will generate a DVD image that you can either boot a VM from or burn to a DVD.
Guide on ubuntuforums.org