If you watch Top Gear there is one presenter who does the nerdy bits while the other 2 enjoy themselves with the speed. But for some reason they decided to give James May (Captain Slow) the job of testinga Bugatti Veyron, to prove it really can do 407 killometres per hour. To do this he needed to go to the VW tesing track in Germany where they have an impressive 5 mile straight. James preceded to take the car into the straight at 200kph and then dramatically take this wonderful car up to over 400kph.
It was a fantastic peice, even compared to the previous test of racing a light airplane over Europe in the Bugatti, becuase even though they did not mention it at the time, they needed to stick to tthe speed limits.
So the answer is, yes the car really can do 407kph, ven if it is for 12 minutes only as you may run out of fuel and the tyres can only last 50 minutes or so also.
Here is the Top Gear Clip.