NEWS 2000Zap2it reports that the Simpson episode with King will air on November 12. Here is what they say:
Drew Barrymore provides the voice of Sophie in the "Insane Poppy Clown" episode Nov. 12. Bart meets Sophie while waiting in line to see Krusty at a book festival and she reveals that she is Krusty's daughter -- a product of a one-night stand he had during the Gulf War with a special forces commando. Hoping to make up for lost time, Krusty looks to Homer for parenting advice. Stephen King also guest stars as himself and Joe Mantegna reprises his role as Fat Tony.
The Simpsons Archive reports that the episode of The Simpsons where Stephen King and Drew Barrymore are lending their voices has been pushed forward and will not air until the series 12:th season. This means that it will air on FOX sometime between the premiere (September or October 2000) to mid-season 12 (early 2001).
Here is an article about it:
THE SIMPSONS GUEST VOICES
Writer Stephen King, teen pop singer Britney Spears and actresses Drew Barrymore and Betty White are among the upcoming guest voices on The Simpsons.
Don Cheadle provides the voice of preacher Brother Faith in the episode "Faith Off," this Sunday. When Homer get his head stuck in a bucket of glue, the family attends the revival meeting of Brother Faith in a desperate attempt to save Homer. Brother Faith calls upon Bart to assist him and when the bucket comes off, Bart is convinced he too is a faith healer.
Spears appears as herself in "The Mansion Family" episode on Sunday, Jan. 23. When Mr. Burns is honored as Springfield's oldest resident, he retreats to the Mayo Clinic while the Simpsons house-sit at his mansion with disastrous results.
King and Barrymore lend their voices to the upcoming "Insane Clown Poppy" episode, in which Krusty the Clown takes parenting lessons from Homer when he discovers that he has a daughter about Bart's age from a one-night stand.
White plays herself in a forthcoming episode entitled "Missionary: Impossible," in which Homer inadvertently joins the Peace Corps.
Other guest voices upcoming this season include musicians Randy Bachman and Fred Turner of Bachman Turner Overdrive, singer Shawn Colvin and rock stars Kid Rock and his sidekick Joe, all of who will play themselves.
The longest-running sitcom on television, The Simpsons also currently holds the Guinness Book of World Records titles for "longest-running prime-time animated series" and "most celebrities featured in an animation series." Celebrating its 10th anniversary, The Simpsons also will receive a Star on The Hollywood Walk of Fame on Friday."