His rising status was further confirmed when he was signed to star opposite Leelee Sobieski in the romance "Here on Earth" (2000). Klein subsequently headlined the low-brow incest-themed comedy "Say It Isn't So" (2001, produced by the Farrelly brothers) and was tapped to star in the remake of the 1970s actioner "Rollerball" and appear in the ensemble of the Vietnam-era drama "We Were Soldiers" (both 2002), the true-to-life telling about the Air Calvary’s landing in the Ia Drang Valley on November 14, 1965—the first major, and perhaps bloodiest, battle of the Vietnam War. In “The United States of Leland” (2003), Klein was the boyfriend of a girl (Michelle Williams) whose autistic brother is stabbed 20 times by an alienated teenager (Ryan Gosling). He then had a supporting role in “Just Friends” (2005), a mainstream comedy about a suave music executive (Ryan Reynolds) whose former life as a shy and overweight high school senior is resurrected when he runs into the best friend (Amy Smart) he had a crush on.