http://torchrelay.beijing2008.cn/en/journey/map/
Apparently the torch (or to be more specific "a guarded flame") travels ~85,000 miles around the world before the games start, it does this using various modes of transport including it's own Air China jet and ~20 vehicles provided in each relay city.
There were no torch relays in ancient Games, the Nazis decided it was a good idea in 1936.
Seems a bit wrong to be wasting all this energy at a time when "green" is so important to the world don't you think?
Further reading:
http://news.bbc.co.uk/1/hi/world/europe/7330949.stm
http://news.bbc.co.uk/1/hi/magazine/7327079.stm