[Hatzenbach]

To answer seventythree's first question:
The four basic functions provided by the four wires are:
* Up/Down (scroll through trip computer / temperature / dist to empty / MPG)
* Set the chime to ring at a certain speed (you first enter this mode and then set the desired speed with the up / down buttons)
* Cancel / Reset (for that you must press the button for like 3 seconds)

Now about the OBD in the Boxster clusters
The original cluster was made by Motometer and was available until (as far as I know) 2001 and had a small and very basic LCD display.
With the 2002 model Porsche switched to a (very similar looking) cluster made by VDO for both the 986 and 996 (the 996 Turbo got the newer cluster with the 2001 model)
The VDO cluster had bigger areas for the LCD and as far as I know had a more basic LCD module in the 986 and more fancy in the 996 (which had a full blown dot matrix pixel display).
The 986 display had two rows of numbers:
mileage on top
trip computer / temperature / dist to empty / MPG on the bottom

So far I was under the impression that the "fancy" display which has three rows (where the bottom one is bigger) was only available in the 996 but apparently I was wrong.
Nevertheless, have first a look at the elements in your center LCD display. If you see distinct elements like you would see in a digital clock, then you have the "simple" display, if you can not see distinct elements, then you have the more fancy dot matrix display which should be able to display all of the features in your manual.

Oh yes, and I should mention that I got all the functions in seventythree's manual to work in the 996 cluster in my car with the four wires from the OBC hack.