No. The CPO of the car should have done the same things as a PPI. I would ask to get a copy of the sheets that the dealer filled out when doing the CPO inspection that they transmitted to Porsche to get the approval for the CPO.
The 2000 has just enough miles on it per year that it shouldn't be suffering the ills of an undriven car. But the CPO on it will expire much sooner in terms of time than the CPOs of any of the others.
How many miles per year are you going to drive this car? That should help you figure out if time or mileage is the more important factor in when the CPO expires.
CPO is 7 years from the in-service date of the car and (for example) a 2000 model year could have an in-service date as old as September 1999. So ask the in-service date for the 3 cars and don't judge the CPO length by the model year.
The 2003 is more desirable (look at the list of model year changes on my web site) but only you can determine if the additional miles and additional CPO time and additional improvements are worth the additional $ taking into account differences in condition and options. Any of the cars and years will give you years of fun driving.
Tips on buying a Boxster are among the web pages there too, look in the index.
http://mike.focke.googlepages.com/modelyeardifferences