From Entertainment Weekly:

CHUCK: Guest star Nicole Richie–yes, that’s her–guns for her old high school nemesis Sarah Walker (Yvonne Strahovski, not pictured), Chuck’s CIA gal pal, on an October episode of the NBC spy series.

“She was a cheerleader,” says Nicole of her character, Heather. “Kind of that b—-y mean girl.”

Looks like old habits die hard.

“I had a stunt double,” added Nicole on her action-packed role as a girl girl on NBC’s Chuck. “But they said I was allowed to do as much as I wanted–except for serious things.”

Read more at: http://justjared.buzznet.com/2008/07/18/nicole-richie-chuck-first-look/.