Steven Novella (from The Skeptics Guide to the Universe podcast fame) blogs on the study over on Neurologica as well which is cool.
Anyhow, one of the interesting pieces in this research was the use of "The Getaway" PS2 game which models the London streets. This allowed the taxi drivers to mimic their usual work function including the navigation while strapped into an fMRI scanner.
A quote from the press release:
In a follow-up study, Dr Spiers and Professor Maguire used the Playstation2 video game "The Getaway" to examine how taxi drivers use their hippocampus and other brain areas when they navigate. Taxi drivers used the virtual reality simulation to navigate the streets of London whilst lying in an fMRI brain scanner. The researchers found that the hippocampus is most active when the drivers first think about their route and plan ahead. By contrast, activity in a diverse network of other brain areas increases as they encounter road blocks, spot expected landmarks, look at the view and worry about the thoughts of their customers and other drivers.
[Screenshots from The Getaway via the Gamespot site]