Gillian didn't play anything for the first 40 seconds, then she launched that arpeggiated figure; the string synths on top of that bit were sequenced, I think. Then on the chorus she played the string synth chords. In the early live performances she followed that with a short solo of sorts before the second verse. Repeat the process a couple of times and there you go.
Still can't remember if Steve played anything other on it than the choir samples, he might have done the arpeggios in the verses. But then I haven't been watching the later performances on DVD for a while anyway. Not that it matters. His main job during the song has always been to shake his ass while standing next to the keyboard. ;)
(That's how I've seen it on the few live DVDs I have, I might be wrong in part though!)