(Portland, OR)  --  Comedian Katt Williams is pleading not guilty to an assault charge after being arrested Saturday in Portland.  Williams appeared in a Multnomah County courtroom yesterday on a charge of fourth-degree assault.  Williams is accused of attacking a private town car driver Friday after arguing about taking him and his dog to a scheduled performance in town.  The driver was treated at a hospital for minor injuries.  Police say Williams is also being held on a "fugitive hold" for an active warrant out of Georgia.