Who is at fault when a car hits a driver that has just changed lanes because the car was speeding?

Who changed lanes? Not sure I understand, am going on the assumption you changed lanes, but hit the other party because they were speeding. You have a duty to not change your lane unless and until it is clear and safe to do so. If the other driver were speeding (and you can prove it) there would be some negligence assessed to the speeding driver. This is difficult to prove though. If you'd like to give me more details, then I could be of more assistance.