Well, bagged(live sand) may be live when they first package it and retail it.. but over time as the bagged sand sits around on shelf-life, all living matter dies off because of temperature changes, handling, etc.. So when you buy the "live sand," you're actually buying sand with dead things in it. lol.
As it was previously said, you are better off buying dry aragonite sand and starting off nice and clean. Over time, the things living in the live rock you bought will begin to inhabit the sand and then it will become "live". It will take a while though for your sand to be considered completely "live" so we shouldn't be expecting any miracles lol.
But all in all, you'll see over time that it was in your best interest to just start off with new fresh sand.