You would think it would be easy - start at the bottom and finish at the top. Pah. Luckily there is one start line (although the 2004 Tour de France start line for the Time Trial was slightly further forward apparently). Here is a picture of the current start line, just over a picturesque stream and next to a rather bleak EDF outbuilding.
Le grand depart...Then things get decidedly interesting. The "Unofficial" (?) or popular finish line is next to the Tourist Office and has a white line painted on the road and a banner with Arrivee in big red letters. There's even a 1-2-3 podium beside the road for those commemorative photographs (Although Photobreton takes a good snap just before switchback 1, and theres another outfit taking photos at switchback 5).
The tourist finish...Since in July 2007 there are some roadworks along the Tour de France finishing stretch there is a temporary Tdf Finish line painted on the road just before the last roundabout.
The "temporary" Tour de France finish line...Looking up the finish line on July 2nd 2007 you can see there are plenty of roadworks but the finish straight is open for access. There isn't a finish line marked on the road but once you get to the end of the roadworks you're pretty much there. Bit of an anticlimax I have to say - and a pretty rubbish photo opportunity!