It's not insane to implement IDE/ATAPI and a FAT filing system. I've
been thinking about doing the same thing. Interfacing to IDE is pretty
simple. ATAPI is more involved, but not terrible.

The first FAT reference that comes to my mind is in "The Indispensible
PC Hardware Book." I'm sure you can find other references on the web.
Dave Dunfield (http://www.dunfield.com) has some old PC based code
for implementing the FAT and basic I/O routines on a floppy. It's a
bit different with a hard drive, but it's a good starting point.

Although lots of people will point you to the Linux source code, I'd
ignore it. It's too Linux specific, with all sorts of inode junk.
You're best off reading up on the way the disk is structured under
DOS/Win95 (Win95 adds a few extensions) and looking at the Dunfield
source.

Regards,
Jeff