Many vegetables are actually better for preventing bone loss than cow’s milk. Preventing osteoporosis is about more than calcium intake. It is also about calcium absorption and the calcium in many vegetables is more absorbable than calcium from cow’s milk. A number of vegetables also have more calcium per calorie than dairy milk and vegetables have other nutrients for bone health that dairy milk does not.

Highlights from page 103 [of Brenda Davis's "Becoming Vegetarian"]:

Cow’s Milk
1 cup – 300 mg – 32% absorbed, 96 mg net

Turnip Greens, cooked
1 cup – 198 mg – 52% absorbed, 102 mg net

Bok Choy, cooked
1 cup – 158 mg – 53% absorbed, 84 mg net

Mustard Greens, cooked
1 cup – 128 mg – 58% absorbed, 74 mg net

Kake, cooked
1 cup – 122 mg – 49% absorbed, 60 mg net

Broccoli, cooked
1 cup – 70 mg – 61% absorbed, 42 mg net

Tofu, made with a calcium based coagulant
1 cup – 516 mg – 31% absorbed, 160 mg net

Taken from: change.org: On Lactose Intolerance and Absorbing Calcium.

Go Vegan!