SHE HAS DONE YOGA, running and Pilates, now Courtney Thorne-Smith is all about multitasking: She simultaneously works out, catches up with pals and exercises her pooch during her regular walking sessions near the modern Los Angeles home she shares with her fiance, physician Robert Andrews, 38. Here she walks Us through her routine.

What she does Two to three times a week, Thorne-Smith heads out for a sweat-inducing hike through Mandeville Canyon, a hilly park in her neigborhood. "I walk for an hour or two with my friends, Mary [Gilmer, 43, a stay-at-home mom] and Jean [Mortimer, 43, a business owner]," says the five-foot-six actress. "But on other days, I'll go at six in the morning with Ed, my 12-year-old basenji. The dog is always running, trying to get me to speed up. If I'm well-rested, I go pretty fast, about four miles an hour."

What it does for her body "Walking makes my legs longer and leaner, and it firms my thighs more than running," says the According to Jim star, whose usual routine culminates with a steep uphill climb. "It's a butt-killer at the end, but the results make it worth it!"

Why she loves it "Walking clears my mind," says the actress. "I love this path in particular because Robert proposed to me here on Thansgiving Day 2002. We went out at 6:15 A.M. and even after walking and walking, Robert wanted to go farther. It turns out he was waiting for it to get light so I could see the ring! He finally proposed to me by this tree that I see every time I walk the dog. It's very sweet." (Thorne-Smith and Andrews plan to wed this summer)

How she fuels up "I'm a healthy eater," says Thorne-Smith, who revs up for walks with green tea. Post-workout, she'll have some fruit, followed by a salad for lunch and salmon for dinner. "But now that I am older, I don't have a strict diet," says Thorne-Smith. "I just try to stay well and happy."

Her Stay Fit Secrets �Workout tapes To fit in fitness at home, Thorne-Smith relies on her favorite videos: Winsor Pilates, set of four ($40; winsorpilates.com) and Ali McGraw: Yoga Mind and Body ($12; bn.com). "I do something everyday." �Weight lifting "I like to use 5-, 10-, and 12-pound dumbbells a few times a week to build strength," says the actress. "I love to feel strong." �Popping produce "I eat mostly fruits and vegetables," says Thorne-Smith. "Right now, I'm into hummus." While she shuns starchy foods (like bread), the actress admits to a sweet tooth. "My new thing? Dum Dum lollipops."