The Insane Clown Posse is among five new acts that have been added to the lineup for Woodstock ’99. The group, along with Buckcherry, Oleander and Moby, will join performers such as Alanis Morrisette, the Dave Matthews Band and Sheryl Crow at next month’s event, promoters said Wednesday. Another new act tapped to perform is The Umbilical Brothers, the acclaimed creators of off-Broadway’s “Thwak,” a show that combines comedy, mime and audio effects (and does it hilariously). Woodstock ’99 is scheduled for July 23-25 at the old Griffiss Air Force Base in Rome, N.Y. Organizers say they expect as many as 250,000 people.