if you want to make a background disc all you is
get a blank cdr (not dual layer, and not a dvd +/- r, just a regular old CD-R)
find a file that is 100MB or more on your hard drive (NO mp3 files)
find the files that you want to use for backgrounds
in your burning program, create a folder named "BG"
put the pics in the BG folder, put the 100MB on the disk also (NO mp3 files)
and that's it. burn it.
I used a CD-RW because I want to be able to change the pics at random. I loaded up the CDRW and then put some backgrounds in the N3. I forgot some pics, so I went back to the computer, put some more pics on the disc, re-burned, and bam, back to the car to put in the other backgrounds.
NO mp3s
no dual layer dvds
no dvd +/- r's
easy as pie.