This is a great video tutorial series to understand rootkits by Corey Nachreiner.

Rootkits Part 1
Corey defines rootkits, then demonstrates a real rootkit found in the wild. See what investigative processes it hides from, how an attacker configures it, and more.
http://www.watchguard.com/education/video/play.asp?vid=root1-cubecast

Rootkits Part 2
Corey explains inline function hooking, what kinds of Windows functions are susceptible to hooking, and how rootkits use hooking for backdoor access to your network.
http://www.watchguard.com/education/video/play.asp?vid=root2-cubecast

Rootkits Part 3
Topics chosen by user vote. Kernel mode rootkits; leading techniques and tools for detecting rootkits; how your Firebox helps stop rootkits from entering your network.
http://www.watchguard.com/education/video/play.asp?vid=root3-cubecast

Very interesting. Thanks for sharing