What is the biblical basis for the Immaculate Conception?

According to Catholic Doctrine, the Immaculate Conception refers to the teaching that Mary's own conception (not that of Jesus) was without the stain of original sin. What is the biblical basis for this? And if this is true, did Mary not need to be saved from her sin? Was she also sinless? If she were sinless, then why would she have suffered the consequences of sin--that of death?