EL PASO, Texas — Equipped with a sniper rifle and shotgun, a Spartan II soldier takes one furtive step at a time under a blistering sun, trying to elude the enemy. Suddenly, he sees an enemy soldier and he goes to fire his weapon — but it’s too late — and a kill-shot to the head drops him on the spot. “Headshot,” the sniper yells out as six friends — all in their 20’s — in two teams of three players battle in the virtual warfare of Halo3. Playing video games, a way of life for the six of them, dominates their free time. But parents and doctors wonder if this behavior amounts to a dangerous addiction or just social interaction.