Question: Does anyone know the name of the composer who wrote the actual music performed by Lizzie and Georgiana as well as music for the movie itself?
Question: Why is there an alternative U.S ending (special feature on the UK DVD version)?
Answer: In previews to American audiences there were lots of comments that it was not a good ending (not romantic enough) so they filmed an ending with Darcy and Lizzie kissing to make it more romantic. The ending in other countries matches the original ending of the book.
Answer: The composer is called Dario Marinelli, the pianist is Jean-Yves Thibaudet. Marinelli composed the music that Lizzy and Georgiana play. The only thing he hasn't composed is the piece that Darcy and Lizzy dance to at the Netherfield Ball, which is a piece from Henry Purcell.