To determine how prior therapy with alendronate or risedronate in postmenopausal women with osteoporosis influences the clinical effectiveness of teriparatide; The primary objective of the study is to compare the teriparatide (human, recombinant PTH[1-34])-associated change from baseline in a marker of bone formation, N-terminal propeptide of type I collagen (P1NP), between subjects previously treated with risedronate and those previously treated with alendronate.