Ottawa Canada Linux Users Group recently hosted another of its Kernel Walkthrough tutorials given by Bart Trojanowski. The screencast starts with a one-hour presentation on the components involved, and then dives into the code which bootstraps the kernel on the 32bit x86 platform. The first Kernel Walkthrough by the Ottawa Canada Linux Users Group covered Linux development background, file layout and data types.
Although you really need some deep understanding of operating systems, and about the ins and outs of x86, I can recommend this screencast.
First the bootprocess of linux is introduced in a theoretical manner, and those claims are then hardened by showing of the code that actually does the stuff.
So whoever wanted to know how linux boots, should definitely watch this.