If you have the film, shazam it Call 2580 on your mobile, hold it to the music until the call ends itself. After about 5 seconds you will receive a msg saying the artist and title of the song. Costs 50p plus standard msg charge.
....or go to iTunes, either find the OST album on the Music Store or have the tracklisting of the OST to hand (play.com), and then go through the 30 second samples of each song until you recognise it. Bit of an ordeal, but cheaper than Shazam (although I have noted that number for my own future reference!)