Allyson Witherspoon, Infiniti USA's new director of marketing, communications and media, talks about where the ad account for the luxury auto brand is headed. The account has long been held by TBWA Worldwide. Nissan is handled by Nissan United, the new Omnicom conglomerate in NYC. The challenge is that many still view see Infiniti cars and SUV's as up-market Nissans. Some keys to the Infiniti ad account are at the jump.