Didja see the little Glee preview that aired during American Idol last night? If not, check it out below. The clip features a snippet of the much-anticipated Madonna episode (scheduled to air on April 20), though Glee‘s first new episode of 2010 will premiere on April 13.

And what can we expect from season 1, part 2? Glad you asked …

1. Tony Award winner (and Mrs. Taye Diggs) Idina Menzel will join the cast for the final nine episodes of season one, as the director of Vocal Adrenaline, the Glee gang’s rivals. Menzel is also a possible love interest for Mr. Schuester (Matthew Morrison) … the words “big makeout scene” have been used to describe one of her interactions with Mr. Schu.

2. Although … the preview clip seems to show Mr. Schu about to lock lips with guidance counselor Emma (Jayma Mays). Let’s hope that’s not a fantasy sequence or part of some musical number.

3. About the Madonna ep: It may include as many as 10 Madonna songs, including Sue Sylvester’s (Jane Lynch) version of “Vogue” (gotta love her in the cone bra in the preview), Rachel’s (Lea Michele) “Express Yourself,” and, very appropriately, preggers Quinn (Dianna Agron) singing “Papa Don’t Preach.” “Like a Virgin,” “Crazy for You,” “Borderline” and “Open Your Heart” are rumored to also be among the tunes.

4. Michele’s Spring Awakening co-star Jonathan Groff will guest star as Jesse, a Vocal Adrenaline-ian.

5. Best rumor: That Neil Patrick Harris will guest star in an episode of the show, which is being directed by Buffy the Vampire Slayer daddy – and NPH’s Dr. Horrible’s Sing-Along Blog cohort – Joss Whedon.

6. Jennifer Lopez as a cafeteria worker? Series creator Ryan Murphy says he’s talking to J. Lo about playing a cafeteria worker who gets a glam makeover and, as a result, looks like, well, J. Lo. Is it too much to hope that snippets of Adam Sandler‘s “Lunchlady Land” will fall into the mix?

7. Olivia Newton-John + Sue Sylvester = Performing Newton-John’s classic ’80s tune “Physical” … it’s happening in an April episode of Glee. “Physical,” by the way, was just named the sexiest song ever by Billboard magazine.

8. If you missed the cast’s big promotional tour last year before Glee premiered, get ready to purchase tickets this summer, when Gleeks everywhere — actually, in select cities — can buy tix to the Glee summer tour. Scheduled stops so far include New York, Los Angeles, Portland, Dallas and Orlando.

9. Still more guest cast news: Former Saturday Night Live star Molly Shannon will play a teacher/badminton coach/big user of pharmaceutical enhancements who tussles with Sue Sylvester. Shannon is scheduled for a May episode.

10. And re: storylines, rumored happenings include Quinn having her baby, Rachel getting romantic with Puck (Mark Salling) again, Terri (Jessalyn Gilsig) not giving up on her marriage, the revelation of some info on Puck’s home life and Sue once again torturing poor Principal Figgins (Iqbal Theba).

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