you can also buy software to plug your laptop or palm into the diag port of the Boxster.
http://www.autotap.com/orderonline.html
as far as OBD II scanners its pretty simple. Plug it inot the port under the dash nearest the driver side door. The computer links to the scanner after about a minute it displays the error code that triped the Check Engine Light to come on.
It can be a great stress relief to find out where the problem is coming from quickly,
like the dork that didnt screw on my gas cap all the way (short of 3 clicks) no self service allowed here in New Jersey. Filling up while the engine is running can trip the CEL light as well. Turn the car off take off the gas cap screw it back on (at least 3 clicks) and the CEL light should stay off. The OBD II will allow you to erase the code and the CEL light will turn off.
If the CEL is blinking you've got big problems and should park, turn the car off ASAP and call Triple AAA.
The scanner, a print out of the error codes and a small fuse checker(with some spare fuses) are great tools to have in that rear compartment.