I believe that the Chicago Tribune (or some paper) did an article about hte similarities and differences a very long while back. But here's some of the basics:
The whole coconut thing, the French castle and Trojan rabbit, the knights of Ni, Robin's minstrel's, and Prince Herbert are all in there. The Lady of the Lake and her Grail Girls are added. The first act sticks mostly to what the average Pythoner knows (though, there is a very new take on what kind of place Camelot is), while the second act goes off in all sorts of strange directions. Its different enough, without being too different.
"I mean, how many of us could honestly say that at one time or another he hasn't set fire to some great public building?"