Here are a couple of Mountain Biking books that you might enjoy:

William Nealy's Mountain Bike! A manual of beginning to advanced technique This book is illustrated with some very charming cartoons -- educational and entertaining!

Mountain Bike Magazine's The Complete Guide to Mountain Biking Skills This book has a series of articles. The beginning has a great story of a roadie getting his first taste of mountain biking -- something most of us can relate to.

Have fun!

-- Melissa