Here's an article written by Ken Dunham on Rootkit. It starts talking about what a rootkit is and it ends with an anti-rootkit test, a comparative test between the most used anti-rootkit programs out there. I just don't know how to trust this kind of test, however, it's a nice reading.

http://www.sans.org/reading_room/whitepapers/honors/1761.php?portal=fc0801ff5339d49ef56c196d7d2965e4