Originally Posted by RWood
A nested TOC is not possible in a Sony UI using only the buttons.
Yes, it is, with a PDF file. You can also create nested TOC in epub files: when Adobe DE will be available on the PRS-505, it'll be another way to get nested TOCs.
Concerning those links pointing to other books: never heard about this on the Sony. In theory, it's possible with Mobipocket files, but it only works with Mobipocket Reader on Windows, not on the Cybook or on the Kindle.