If it's not the fan belt it's most likely to be, as you say, one of the pulleys. They don't normally squeal, but if one of them was (partially) seized, the belt would squeal as it went over it. Any problems with any other systems on the car (e.g. power steering, aircon, battery not charging?). If so, the relevant pulley for that item could be seized.
John, February 2008