A fellow poster had this to say about visiting Versailles and Chartres in the same day:
"The palace opens at 09:00 and the first fountain display is 11:00-12:00. Since everyone's pace is different, I don't know how rushed you'll feel trying to see both the palace and Marie Antoinette's home in two hours. However, you could go back after the fountain display to see what you missed and still get to Chartres in time to visit the cathedral. Visiting hours end at 19:30. Guided lectures in English by Malcolm Miller are at 12:00 and 14:45. If you want to visit the crypt, beginning on 1 April the scheduled times are 11:00, 14:15, 15:30, and 16:30.
On Saturdays there is once-an-hour train service from Versailles-Chantiers to Chartres. Trains depart at 47 minutes after the hour."
What do you think? Is this feasible?