When Marilu Henner and Kim Fields both flip the bird at a camera crew following around Lisa Kudrow (search), you know you're watching HBO (search).

Their unpixelated middle fingers make their unforgettable appearance during the premiere episode of former "Friends" star Kudrow's new HBO series "The Comeback," (search) debuting Sunday at 9:30 p.m. EDT, following the second-season premiere of "Entourage."

The two former sitcom stars — Henner, 53, of "Taxi" and Fields, 35, of "The Facts of Life" — encounter Kudrow, 41, at an audition where they're all up for the same part on a new network sitcom.

Kudrow comes with a camera crew in tow because she's also starring in her own reality show — a reality show within a reality show that's also titled "The Comeback."

It's not as confusing as it might sound.

Without giving too much away, here's what Kudrow's widely anticipated show — the second one, after NBC's "Joey," to feature one of the six former stars of "Friends" — is all about.

On "The Comeback," Kudrow doesn't play herself; she plays Valerie Cherish, a television actress who last starred in a prime-time comedy on an unspecified network back in the early '90s. The show, called "I'm It!," lasted four seasons.

Cut to the present day, and Valerie is trying to get back into series television. To do this, she agrees to allow a camera crew to follow her around for a reality show that the network (still unspecified) wants to air as a companion to Valerie's new sitcom.

It's at an audition for the sitcom, titled "Room & Bored," that Valerie and her camera crew confront Fields and Henner in the waiting area at a casting agency.

Fields and Henner also have camera crews following them, they say, but both have agreed to dispense with the cameras during the audition process. However, Valerie refuses, which draws the middle-digit reaction from the two other actresses.

In "Room & Bored," Valerie plays one of four female roommates living in a big-city apartment. But when it comes time to film the pilot, that scenario suddenly changes.

In Episode 2, Valerie is on her way to New York for the network "upfronts," the annual mid-May presentations where the network honchos, assisted by their series' stars, unveil their new fall lineups for the advertising community.

In its own way, "The Comeback" does for the world of television what "Entourage" does with the movie business. Both shows are send-ups of their respective sectors of the Hollywood-based entertainment industry.

Incredibly, TV fares far worse in "The Comeback," where the biz comes across as meaner, colder and shallower even than the movie industry, if such a thing is possible.

For Kudrow, "The Comeback" seems to present a much stiffer challenge than "Friends" ever did.

She more than rises to it, however, and in the process, says farewell to Phoebe.