Movie Question: The Sweetest Thing?

I know I've heard this song before and I know I should know it. I'm pretty sure I have it on my iPod but I don't feel like going through all my classical music. What I'm asking is what is the song playing at Peter Donahue's wedding in the movie The Sweetest Thing? It's a common classical score. I know it's like Mozart or Beethoven... somebody like that. I just don't remember. Anybody know who it is or what the name of the song is? Thanks!