2003 mustang 3.8l v6

Well, went to go to work yesterday morning and the second i started the car it made a horrible squeaking noise then it began to misfire then stalled. ran perfetly fine the night before. After popping the hood I Tracked down the general area it was coming from and it seemed to be around the alternator and idler pulley. I know both of these can cause the sqeaking but can either cause the misfire and stalling? Or can this be something else?

 

Sounds like one of the pullies has seized up. Get someone else to start it while you're looking at them. Fix the dud