Ray Liotta's real-time tour de force as a dying alcoholic defibrillated ER's ailing ratings in November. So it's no shock that the NBC medical drama has lined up more big-name guest stars for February sweeps.

First up, on Feb. 10 is Sissy Spacek, who'll play the long-lost birth mother of Dr. Kerry Weaver (Laura Innes). How did ER land the Oscar-winning actress? "I'm a huge fan of [executive producer] John Wells," Spacek says. "We worked together on [the 2004 indie film] A Home at the End of the World, and since then, he's been sending me ER scripts. This one just spoke to me."

"The show has a pretty solid reputation for actors and if it didn't have that, we would've never had a snowball's chance in hell of getting her," executive producer Dee Johnson says frankly. "As far as I know, [Spacek appears in only] one episode, but it's not like she drives off a cliff at the end, so nothing's impossible."

One week later, Sex and the City's Cynthia Nixon shows up as a soccer mom who suffers a stroke. The twist that hooked Nixon: Her character can't speak, but viewers will be able to hear her thoughts.

"You can really dig into a character on this show," Johnson adds. "You're in a life-or-death situation — it doesn't get much more dramatic." Or more Emmy-friendly — and for actors, that's just what the doctor ordered.