Encryption and Archives
Tinke
This is a great tool for extracting the contents of your ROM. It also supports reading a number of Nintendo DS formats and should be able to interpret much of the game's graphical data after decrypting and decompressing with Zipper. While it does support .narc files, the .narc files in Phantasy Star 0 are encrypted and compressed as well and will need to be run through Zipper before viewing.
Zipper
A simple tool for extracting .zarc and .narc archives as well as decrypting and decompressing loose files, however it does not retain the archive's folder structure per file. Optionally, it can dump the processed .narc archives for extaction with another .narc tool in order to retain these.