lovely chinese soundtrack I ever hear that before

The Soundtrack album is Chinese Odyssey 2002 Original Motion Picture Soundtrack released by EMI

the one they singing while drunk is

Zuìyīchǎng (醉一場; "A Drunk Song" ) [2:24] by Faye Wong and Tony Leung

you could find the track list on wikipedia
http://en.wikipedia.org/wiki/Chinese_Odyssey_2002