I don't know how to become a vegetarian, but I know how to become a vegan.
Here are some resources that were helpful to me:
How to Become a Vegetarian, the Easy Way | zen habits http://www.petaliterature.com/VEG297.pdf (pdf)
PCRM >> Health >> Vegetarian Starter Kit http://www.veggie123.com/veggie/readourebook/ How can you start?
"Becoming Vegetarian" is a decent place to start if your library has it, but I wouldn't bother buying it.
The first thing that my wife and I did was take our regular meals and just cut out the animal products. One example is spaghetti. Spaghetti sauce with meatballs became plain spaghetti sauce, with no cheese. Later we started putting things in the sauce to make it interesting (and more healthy): broccoli, spinach, beans, zucchini, etc.
Of course, there are also a bazillion vegan recipes on the web.
vegan recipes - Google Search