DietCoke.com has posted the first of 13 Webisodes of an original Internet series called “What’s Your 20?” about a Hollywood production assistant struggling on a film shoot in Montana.Both the soft drink’s Web site and the online series bowed this week. Series hopes to tap into Diet Coke drinkers’ interest in all things entertainment. The company also has inked promotional deals with the Blockbuster Entertainment Awards, Sony.com, VH1.com and AOL Moviefone.com to appear on the site. Essential Entertainment produced the online series. Deal follows similar moves by Abercrombie & Fitch, the Army, BMW, Ford, Skyy Vodka and Volkswagen, among others, to broadcast short films or Web series on their official sites, with content coming from AtomShockwave.com or iFilm.com, among other sites.