The primary objective of the study is to determine whether treatment with zoledronic acid at the time of initiation of androgen deprivation therapy for metastatic prostate cancer will delay the time to first skeletal related event. The secondary objective of the study is to compare the effect of treatment with zoledronic acid to placebo on overall survival (OS), progression-free survival (PFS) and toxicity in men receiving androgen deprivation therapy for metastatic prostate cancer.