This instructable describes how to charlieplex a bunch of 7-segment led displays.
Charlieplexing of discrete leds has been the topic of a few other instructables. The Charlieplexing LEDs- The theory
and the How to drive a lot of LEDs from a few microcontroller pins
comes to mind. They are both excellent and should be read by anyone that wants to gain a deeper knowledge of how charlieplexing really works.
Charlieplexing 7-segment displays is more or less the same as doing it with discrete leds, but with some changes to handle the fact that all the led segments have a common pin instead of being separate, and the need for buffering of the common output so the poor microcontroller can cope with the load.