As I understand it, the MAP sensor does correspond to boost. I believe that your year had a separate MAP sensor specifically to read that. The 2000+* only have one, so my knowledge there is limited. This is another description of the operation of the MAP from a '98 Regal GS.
Description and Operation
The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure. The PCM supplies a 5 volt reference and ground for the MAP sensor. The MAP sensor circuit provides a signal to the PCM relative to pressure changes in the manifold. With the key ON, engine not running the MAP sensor signal voltage to the PCM varies between 1.5 to 2.5 volts. With the engine running, the MAP sensor voltage to the PCM varies from below 2 volts at idle (low manifold absolute pressure - high vacuum) to above 4 volts at wide-open throttle (high manifold absolute pressure - low vacuum).
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.