The latest version of this mini-HOWTO can be downloaded from my homepage in several formats (including SGML and PostScript.) The document has been translated into Japanese by Mr. Teruyoshi Fujiwara as part of the JF project.
Gregor Hoffleit maintains a homepage with information about the developement of U2FS and UFS.
The FreeBSD Project Homepage has a lot of information about FreeBSD (besides the whole system ready for download.)
The Linux Kernel HOWTO is released as part of The Linux Documentation Project.