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Newsday.com

Neil Patrick Harris, Britney Spears

Neil Patrick Harris, left, as Barney and guest star Britney Spears as Abby appear in a scene from the May 12, 2008 episode of "How I Met Your Mother."

Neil Patrick Harris, left, as Barney and guest star Britney Spears as Abby appear in a scene from the May 12, 2008 episode of "How I Met Your Mother."