Tonight, “30 Rock” has a very special guest star, “Mad Men’s” Jon Hamm. Hamm will star as Liz Lemon’s love interest in a 3 episode arc (over the course of 4-5 episodes). Knowing Liz’s track record in love, we can guess where this going, but it is sure to be a fun journey getting there. He plays a recently divorced neighbor that Liz becomes quite smitten with. Hamm seems like an obvious fit for the show, not only is he classically handsome, but he also stars on another show that is a favorite of critics but can’t seem to gain a large audience. Salma Hayek returns too as the nurse Jack has eyes for. If you want to catch up on ”30 Rock” and see for yourself what all the fuss is about, you can watch full episodes on Hulu, who, incidentally, is using one of “30 Rocks” stars, Alec Baldwin, as their new pitch person.

Before you watch “30 Rock”, you won’t want to miss “The Office”. Michael goes on a speaking tour of other Dunder Mifflin branches accompanied by Pam. The two make a stop at the Utica Branch where they run into a very pregnant Karen (Jim’s ex). Can you say awkward? Later, on “ER”, William H. Macy returns as part of the parade of stars leading up to the biggest guest star of them all- George Clooney!

Over on ABC, tonight marks the first “Private Practice”/”Grey’s Anatomy” crossover. When Addison’s brother, Archer, suffers a sever seizure, she recruits Derek’s help to save him. In the meantime, Derek tries again to ask Meredith to marry him.