I think he'd do better running against the Hildebeast or Upchuck Schumer for a Senate seat in NY!
Ideally, that's what I'd prefer. Rudy running against Hillary in 2006. And come 2008, if another Republican is elected, I'd like to see him as Attorney General.
If Giuliani could beat Hillary in the 2006 Senate race in NY, then we might not have to worry about her running for President. Of course if it looks like he will run for the Senate seat, she could choose not to run for a second term (in order to gear up for the 2008 race).