Why would you want to dump OneNAND data from N900 when you can simply extract the information out of the firmware images which are downloadable from tablets-dev.nokia.com? It is so much safer when you extract the information out of firmware images than extracting it directly out of the device.

The 0xFFFF tool is very handy for such purposes, I cannot see how it does not really help you. Most of the basics of what makes a fiasco image were detailed enough on that site (despite it being old and somewhat outdated as the author lost interest when N900 came about) to give one some insights on the proprietary internals.

The rootfs is a UBIFS type filesystem and the NOLO is a largely closed proprietary bootloader which you will not be able to get far into understanding the whole process without bricking your device.

I personally think that with your vague questioning of your interest and showing the lack of knowledge into file disassembly you will not be able to get far. 0xFFFF tool is a great tool and the author's site has done whatever he could to help anybody interested in the fundamentals despite the outdated information posted on his site.

Assuming you are using windows, with the lack of tools windows provides and given the fact that N900 runs on linux platform you will not get far (hence your lack of understanding of rootfs internals). A standard and decent linux distribution with proper command line utilities will easily help you understand some of the internal structures of the fiasco image. There are tools like file, mount, dd, etc, etc, etc which greatly assists one in doing file disassemblies.

FYI: Nokia's proprietary flashing tool can also extract fiasco images and may also help in identifying parts of fiasco (though very vaguely).