Android Programming: Kernel/OS Development: Need Options/help?

[KING]

I am an UNIX expert (intermediate). I am interested in Android OS platform.
Want to learn more about the OS and kernel. I do not want to develop applications for it. But, I want to be able to modify Kernel/create custom OS (like XDA stuff).

What should i begin with.(any book/weblinks will help)

 

[Gautham]

Since a lot of job to do its better to start reading some books.