If you travel at the speed of light do you go back in time?

I saw a program called the worlds first time traveler on google video look it up to see for yourself and in the program it says you can travel back in time if you were in a spaceship and went around the earth at the speed of light. How is this possible can you explain exactly how it works. I think no matter how fast you could travel you would never go back in time if you went around the earth because the first time you went around the earth no matter how fast it was it was in the past and when you came around the earth again that would be a new time you came around. So how do they think you can go back in time if you went around the earth at the speed of light or faster. Thank you