http://carzero.freeservers.com/
I just completed one this past weekend, and all I can say is WOW! It was definitely the most fun I've had in a while.
Here's what it is, in a nutshell: They give you some maps and directions (some of the directions could be vague, misleading, or incomplete), and you need to figure out where the destination ("checkpoint") is and be there at a specific time of day. The event is timed so that you *should* never need to break the speed limit, and all the roads are paved public roads. There are multiple legs (stages), and you definitely need a navigator to keep track of location and time. However, there are some really fun roads where it's very tempting to go fast.
They start the events in the afternoon and continue into the evening so part of the challenge is driving and navigating in the dark.
There were lots of different types of cars competing, everything from BMWs to a stock Honda Civic. However, it doesn't really matter what car you drive since it's not a "speed" event; success depends mostly on good navigating and timing.
Hopefully some of you can make it out to the next one (March 26 in the Temecula area). As the year goes on, the events get longer and more difficult, so it would be good to attend the first few "beginner" events.