She's been an '80s bimbette (Married...With Children), a '70s career gal (Anchorman), and now Christina Applegate is playing a '60s dance-hall dame in the Broadway revival of Bob Fosse's Sweet Charity (April 2005). Producers thought about Jenna Elfman and Marisa Tomei, but (to borrow from the show's ''Big Spender'') the minute Applegate walked in the joint, they could see she was a gal of distinction. ''I keep questioning it,'' laughs the actress, 32. ''But hey, man, I auditioned, so whatever I did...'' Turns out Applegate is a closet Fosse fanatic -- ''I've seen All That Jazz a gajillion times!'' -- who did her first step-ball-change at age 3. And despite the legacy of flame-haired Gwen Verdon (the original Broadway star) and redhead Shirley MacLaine (the 1969 film), Applegate's Charity Hope Valentine will stay true to her own blond roots. ''I look more like Marilyn Monroe,'' she says. If Marilyn were a dime-a-dance swingin' '60s chick, that is.