Source code
We will provide links to all of the OLPC source code, along with instructions on how to download it from this page in the wiki.
Kernel and GNU/Linux programs
Much of the source code for the OLPC is stored in a "git" repository at http://dev.laptop.org/git/ . You can check out a particular program, e.g. the kernel, with a command like:
git clone git+ssh://dev.laptop.org/git/olpc-2.6
Unfortunately, this requires that you are a developer with access to write to the git repositories there. Even more unfortunately, git documentation is so bad that I can't figure out the simple, obvious command that would let you "anonymously" check out a copy of one of these programs if you *don't* have an ssh account on dev.laptop.org. Meanwhile, you can look at the pretty source code in the web site at the link above.
Other parts of the system are pulled directly from the Fedora 7 source and binary RPMs.
The script used to build the shipping image of the OLPC operating system is called "pilgrim", and it is maintained here: http://dev.laptop.org/git?p=users/cscott/pilgrim;a=summary
Open Firmware (bootstrap ROM)
The source code for Open Firmware can be checked out of its Subversion repository by the command
svn co svn://openbios.org/openfirmware/
More details are at http://openbios.org/Open_Firmware . Documentation is available at http://openfirmware.org.