Sharing car rides around Japan

Does anyone know a website/forum for people looking to share lifts or carpool across Japan? Something where people post where they're going or want to go and you can decide if you'd like to give someone a lift and share the fuel costs. Also in Australia in backpackers & hostels there are always adds for people driving all over the country looking for people to share the costs. Does anyone know where I can find this information when I'm in Japan?

Thanks :)

You're much less likely to find backpackers driving round Japan as it's relatively expensive (the tolls are very high), tricky at times, especially getting around big cities and parking, and the network of trains is so good.

If you do end up taking trains, check out the "seishun juuhachi kippu" (Youth 18 ticket which anyone can use if you are here at the right time of the year, it is very cheap and there is info about it on this site).