I found a great source of information for troubleshooting problems with PT Cruisers.
I also found out that you can query the car for troubleshooting error codes by turning the key from off to on (without actually starting the car) rapidly three times. If it displays "done" there are no codes.
Here are the code definitions: http://www.ptcruizer.com/computer-codes.html
There is also a section on spark plugs, which is right here: http://www.ptcruizer.com/pt-cruiser/spark-plugs.html I think this is my current problem.