ET has a brand-new sneak peek at BRITNEY SPEARS on the set of "How I Met Your Mother." The pop princess plays a receptionist named Abby at Ted's (JOSH RADNOR) dermatologist's office. This marks her first acting gig since appearing on "Will & Grace" in 2006. Britney's episode of "HIMYM" airs Monday, March 24, on CBS. 

Also guest-starring on the show is "Scrubs" doc SARAH CHALKE, playing Ted's new love interest. Sarah's appearance is a one-shot deal at this point in time, because she is still under contract to "Scrubs," so it remains to be seen if she could end up as the mother of his children.