The instructions to get to the cluster is here:
http://www.whiteson.org/boxster/mods/obc/#3
Then, if you want to see the back of the unit, see this page on my web site...
http://www.iwantaporsche.net/cluster.htm
If you look at the second pic down, the bulb is directly under the white sticker with a barcode on it.
The bulbs can be purchased through Sunset Imports in Oregon and even with shipping and handling, will probably be cheaper than your local stealership.