Mercy For Animals is a group that advocates a plant-based diet, and they have put together a comparison of resources needed to support a plant-based diet vs. an omnivore diet.
Note that this doesn't have to be an either-or decision. Even reducing the animal products in your diet can confer health and environmental benefits. You can still enjoy a bacon or burger now and then while making your body and the world a little healthier.
If you're wondering how, they have some great tips at ChooseVeg.org.