If you want to get into OS development, my suggestion would be to start off with very simple "hello world" operating systems. And if you do, boot it from diskette. NEVER EVER modify your HD's bootsector cause you will never be able to boot Windows again unless you reformat it. I recently bought a book on ASM language that goes more into depth with BIOS and DOS interrupts. Something that you will need to master before you start writing an OS. Here are some links that you might be interested in...

http://www.gaztek.org/osdev/
http://www.acm.uiuc.edu/sigops/roll_your_own/1.html
http://www.linuxdoc.org/LDP/tlk/tlk.html(VERY good)