Michael J. Fox says that acting for him, these days, is "like being a right-handed painter and being forced to paint with your left hand."

"You go, `Yeah, I'm artistic, but the lines aren't straight anymore. I have creativity, but I'm not staying within the lines.' "

Since quitting acting full-time in 2000 because of the debilitating symptoms of Parkinson's disease, first diagnosed in 1991 but not revealed to the public until 1998, the "Family Ties" and "Spin City" star has only occasionally acted on TV.

In 2001 he returned for several guest appearances as Deputy Mayor Michael Flaherty in ABC's "Spin City," and in 2004 guest starred as a surgeon with obsessive-compulsive disorder on two episodes of NBC's "Scrubs."

Now the 44 year-old Fox guest stars in three (and a bit) episodes of ABC's "Boston Legal." He plays a business tycoon, Daniel Post, a cancer sufferer who hires the notorious legal firm Crane, Poole and Schmidt to defend him. Post's been sued for corrupting a study for a new cancer-fighting drug by using his insider clout to ensure he was given the non-placebo. Amid the court case he becomes romantically entangled with his attorney, Denise Bauer ( Julie Bowen.)

Fox's first episode "The Cancer Man Can," airs Tuesday. His story arc concludes February 7. All the episodes air 10:01 p.m. EST.

The producers of "Boston Legal" knew since last season of Fox's interest in the show, but it wasn't until now that a suitable role came up.

Executive producer Bill D'Elia says the actor was "number one on a list of one," because "the character was someone that had to have irresistible charm."

"It was kismet — a combination of several events occurring to create perfect karma," says D'Elia, delighted that Fox signed on for the David E. Kelley series, which "often creates these spicy roles" for guest stars.

Fox says he is a fan of "Boston Legal" for a number of reasons, including its "so smart and so funny take" on ethical and moral issues. He also likes the way the show understands the complexities of human nature and that it is not afraid to recognize that "sometimes people are likable and they are corrupted, and sometimes they are incorruptible, but kind of off-putting."

He particularly enjoyed working on Post's brief encounter with Denny Crane, the most notorious of the ethically challenged lawyers, played by William Shatner, a "fellow Canadian."

"I was really pleasantly blown away by him. First of all Denny Crane, is, I think, one of the great creations of television in the 21st century ... and then there's Shatner's artistry, which I think is a lot misunderstood," Fox says, during a phone interview from New York.

Fox — once the cute young Marty McFly in the "Back to the Future" trilogy of feature films — says, "What I loved was being part of the creative process again. Something as simple as being in a night shoot and smelling the smell of carbon lights in the cold air. 'Wow, the smell of the grease paint!' It was nice, and nice being involved with other actors."

Because of the Parkinson's disease, Fox says he "can't show up with a game plan." He expresses sympathy and understanding for veteran showman, Dick Clark, who, though not fully recovered from a debilitating stroke, had gamely co-hosted ABC's "New Year's Rockin' Eve."

"I am not in such a bad position as he, just given the nature of our separate challenges, but I can see what he was going for, and I felt bad for him that he's gotten such a mixed reaction," says Fox.

Because Fox doesn't know how extreme the symptoms of his illness will be on any given day, he had to wing it in suggesting Post's own health problems. "I just show up and do what I can do, and stay true to the emotional arc of the character."

Fox, who won three Emmys for portraying Alex P. Keaton on "Family Ties" and a fourth for playing Flaherty on "Spin City," says he loved it that "Boston Legal" provided "the chance to do one those courtroom speeches — a soliloquy in front of the judge — which in my long and assorted career I've never done. It was so much fun."

Fun though it was, he admits it was physically "pretty taxing," and he doesn't plan to return to acting full-time. Instead, he says, he's always "finding better things to do," particularly spending as much time as possible with his four kids and wife, Tracy Pollan.

He also devotes himself to The Michael J. Fox Foundation for Parkinson's Research, founded in 2000, which has already raised millions in hopes of finding a cure.

Additionally, he's working on a book, a "kind of follow up" to his memoir "Lucky Man."

It's theme?

"I'm exploring the idea of optimism in all it's forms ... What is optimism all about? It's kind of something I've been playing with."