O'Reilly has published a book for Linux users interested in learning to build their own kernels. Linux Kernel in a Nutshell describes how to build and install Linux 2.6 kernels, starting with downloading the source. It was written by well-known kernel hacker Greg Kroah-Hartman.
I think, this book is a starting point when you would like to learn the Embedded Linux for a Microcontroller, also the Real Time Operating System.
Buy Linux Kernel in a Nutshell from Amazon.com