Name of clown or opera about a clown who laughed on the outside and cried on the inside?

Pagliacci.

Name of clown or opera about a clown who laughed on the outside and cried on the inside?microsoft office 2003

Pagliacci

Name of clown or opera about a clown who laughed on the outside and cried on the inside?windows xp professional internet explorer

Pagliacci

Great Seinfeld episode, by the way...Crazy Joe Divloa!
Although as the others here have mention, "I Pagliacci" by Leoncavallo is probably the opera that you want, the same description could apply to the opera "Rigoletto" by Verdi, which is about a court jester. He has several lines about having to laugh all the time, and being denied the most human emotion of tears. Hope that helps.