How do you replace the evaporator for the a/c on a 2000 jimmy? What do you have to remove to "get" at it???

This is a pretty major job. The standard labor time to complete this task for an experienced technician with all of the correct tools and equipment is 6.2 hours.

Here are the steps from the service manual:

CAUTION: Perfom refrigerant recovery and verify A/C system pressure is at or below 0 in.Hg. before proceeding.
failure to do so can result in personal injury.

Disconnect the underhood lamp electrical connector, if equipped.
Remove the hood.
Remove the VCM or the PCM.
Remove the coolant recovery tank.
Disconnect the electrical connectors from the grille mounted lamps if equipped.
Remove the right front headlamp assembly.
Remove the front bumper.
Remove the right wheelhouse panel.
Disconnect the radio antenna cable.
Disconnect the electrical connector for the horn.
Remove the right fender.
Remove the blower motor resistor.
Remove the accumulator.
Remove the evaporator tube.
Remove the evaporator and blower module heat shield mounting screws (Utility).
Remove the evaporator and blower module heat shield (Utility).
IMPORTANT: Retain the evaporator and blower module heat shield mounting bracket for installation (Utility).
Remove the evaporator and blower module mounting bolts and nuts.
Remove the evaporator and blower module from the vehicle.
Remove the six evaporator case section to the blower case section retaining screws.
Separate the evaporator case section from the blower case section.
Remove the evaporator core from the blower case section.