Upon arriving in Los Angeles, Cook landed her first screen role in The Baby-Sitters Club (1995) and played Becky Thatcher in Tom and Huck that same year. Young filmgoers granted Cook stardom after seeing her opposite Freddie Prinze Jr. in She's All That (1999). She played James Van Der Beek's girlfriend on TV's "Dawson's Creek" and teamed onscreen with him in Texas Rangers (2001).
Cook led the band in Josie and the Pussycats (2001), starred in the miniseries Into the West and had a recurring role on "Las Vegas." Her other films include Get Carter (2000), Antitrust (2001) and Matters of Life and Death (2006).