Jonathan Corbet has written an excellent guide for how to participate in the Linux kernel community. (And I heard Amanda McPherson was in on the planning.) I recommend it to anyone who is wondering how to get started contributing code to an open source software project but especially to those coming from a corporate coding background. The guide covers everything from how Linux kernel releases and patches work to how to design a patch that the kernel will take to how to post the patch. Lots of good history, information and howtos.