Is Rudy Guiliani hurting himself with his attacks on Hillary?

No, it is natural to attack your most likely opponent. Reagan once said the eleventh commandment is "you shall not attack another Republican". This really applies to all parties. Rudy is going after the front runner on the Dems side just like Joe Biden is going after Rudy as the front runner. Don't be surprised that there is gonna be alot of blood letting on all sides as the scramble towards the election in 08.