Have a chat with W.Gates,at Redmond.Learn how to make a fortune and corner the world market.Only need thirty years experiance and 100,000 staff.
Seriously,as Scott and Labman have told you the best way to learn about OS code,is to have a look at Linux.It's open source,ie,anyone can 'add' to it.Bare in mind that their are different versions around,Red Hat,Mandrake,etc,all relating to different coders working in that project.You could set up 'My Linux' and get a few close friends to help.Visit
http://www.yolinux.com/TUTORIALS/ and have a browse around.If you can write Linux style code then your laughing.
I for one would use it!!
All the best to you,
Nez.