John Leguizamo John Leguizamo

When the ER on ER gets bustling, things can get a bit cramped, so it's a wonder that new cast member John Leguizamo, known for bringing big and vibrant personalities to life, will be able to contain himself as Dr. Victor Clemente (joining the NBC drama tonight at 10 pm/ET). This is, after all, the man who played drag-queen Chi Chi Rodriguez in To Wong Foo, Thanks for Everything, Julie Newmar and headlined not one but three one-man stage shows (Mambo Mouth, Freak and Sexaholix: A Love Story).

But the role at the top of our mind when spoke to Leguizamo was his memorable turn as the diminutive painter Henri Toulouse-Lautrec in Moulin Rouge — a characterization that required the actor to perform on his knees in almost every single scene. We have to ask, have his joints recovered? "My knees are fine," Leguizamo tells us with a laugh. "It's my lower back that’s still compressed." Luckily, he adds, "they got me a great physical therapist who saved my spine."

In the four years since Moulin Rouge, Leguizamo has been his busy, busy self, appearing — standing, thankfully — in such films as Arnold Schwarzenegger's Collateral Damage and this summer's Land of the Dead. But despite his big-screen adventures, he remains confident that he can fit onto ER fans' TV sets. Probably. "I'm always careful of those times where I'm entering a situation that I feel is sort of a landmark, or there's a certain expectation of behavior," he says. Fortunately, Clemente isn't known for being a mild-mannered medicine man. "He's coming to County General to update them, bringing in a lot of gadgets, new procedures and experimental things." In doing so, Leguizamo notes, "I'm stepping on a lot of toes."

As well as going toe-to-toe with ER's resident hothead. "When you're the kind of doctor and personality Clemente is, people rub you the wrong way. Especially those who are used to being the alpha dog, so Kovac and I definitely run into each other a lot," he shares. "There's a lot of contention there." The men aren't just clashing over the pool of eligible ladies, either. "I want to do a lot of new techniques that Kovac isn't accustomed to seeing, or has only read about. He's much more old-school, so he has a bit of disbelief in them."

But make no mistake, womenfolk will come into play, albeit not quite as much as Leguizamo would like. "There's a lot of flirting going on," he reports with a smile. "And then I get a really sexy, dirty white girl. It's going to be a sexual healing kind of thing." [As reported in this week's Ask Ausiello, Rescue Me's Callie Thorne has been cast as Clemente's old flame from back in Newark.]

If Leguizamo seems jazzed about his first extended TV gig in, like, forever, it's because he is. In fact, there is a chance that he might stick around beyond the 12 episodes he originally signed on for. "We're in those discussions, talking, trying to figure it out," he tells us. "I am having an incredible time. I didn’t expect it to be this much fun. ER is a machine and the machine waits for no one, but there's still room enough for me to be myself."

And the actor's fans would have it no other way.