We still don't know who will play the knights who say ''Ni!'' or how they'll stage the killer-rabbit sequence, but otherwise, most of the details are finally nailed down for the long-gestating Broadway musical version of ''Monty Python and the Holy Grail.'' The producers of ''Spamalot'' confirmed on Wednesday the casting rumors that had been swirling for a week, regarding the all-stars that director Mike Nichols and playwright Eric Idle had rounded up to play the Round Table knights. Tim Curry, who played ''Rocky Horror'''s Dr. Frank N. Furter on Broadway and on film 30 years ago, will star as King Arthur, the role played in the 1975 film by Python's Graham Chapman. ''Frasier'''s David Hyde-Pierce will play the craven Sir Robin (Idle's role in the movie). ''Simpsons'' voice actor Hank Azaria, last seen showing off his assets as the scuba instructor in ''Along Came Polly,'' will play Sir Lancelot (the John Cleese role).
''Spamalot,'' which has been anticipated on Broadway for at least a year, will play at Chicago's Shubert Theater from Dec. 21 to Jan. 16 before moving to the New York Shubert, where it will begin previews on Feb. 7 and open on March 10. Idle wrote the book and the lyrics for the songs, composed by John Du Prez; the play will also keep three songs from the movie (including ''Brave Sir Robin'' and ''Knights of the Round Table''). Idle boasted in a statement that ''Spamalot'' would be ''as good as or quite likely better than any other show with killer rabbits and a legless knight opening on Broadway or in Chicago this season.''