All the examples are by Pietro Braione (schizophonic@tiscali.it),
adapted from Gareth Owen (gaz@athene.co.uk) who in turns adapted it from 
PolyOS bootsector, (c)1997 Jeff Weeks of Code X Software.
I really have no shame! :)

Being some code from other people here inside, I have no idea of which
kind of license they should come with. Any BSD license should work. Of
course you MUST consider the standard disclaimer at
http://web.tiscali.it/ph/prod.html:

DISCLAIMER: the software published on this page is provided "as is",
without even the hope that it will be useful. It is distributed
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. The user MUST be
aware that the use of provided code may, and will, cause damage.  The
author assumes NO LIABILITY WHATSOEVER for damages arising from any
use of compiled and/or source code published on this page.

This is particularly true for these examples, which run at boot time,
where they are able to access (and damage) all the resources of your
computer, and they have *not* been tested. So, run them at your own
risk, but leave me alone. My advice is, run them on a computer which
does not contain any data (a floppy unit is enough), or run them under
a pc hardware emulator like Bochs or VMWare.

You need NASM to assemble the bootsectors and dd to dump it on a
floppy. Under Linux: 

$ nasm bs_xxxx.asm
$ dd bs=512 if=bs_xxxx of=/dev/fd0 #this to dump it on a floppy, or...
$ mv bs_xxxx a.img                 #this for Bochs (set a.img as floppy boot device in bochsrc)

Feel free to write me (schizophonic@tiscali.it)