It's retro week for DVD releases. First up: season 6 of Magnum PI. Tom Selleck starred as Thomas Magnum, a Vietnam veteran formerly with the Naval Intelligence service. Now a private eye with very rarefied tastes, Magnum was hired to handle security for a reclusive mystery writer named Robin Masters, who maintained a lavish estate on the "gold coast" of Oahu. Also on DVD: season 3 of The Rockford Files, season 4 of The Doris Day Show, and season 1 of the the not-so-retro Girlfriends.