while visiting Magic Kingdom 2 weeks ago, I decided to experiment with using an ipod to listen to ride music while on space mountain. It worked like a charm, and you'd be surprised at how many things synced up to the disneyland original soundtrack.
To recreate my experience:
put the Space Mountain (Original Disneyland Soundtrack) on your iPod. Pause it at 24 sec. and push the HOLD button so that you can put the player in your pocket while in line, and not lose the place in music. When you get in the car (keep in mind I was sitting in the very front, on the left side track - facing the load station) while timing this...so it will be more exact if you do it from there), move back the Hold switch so it isn't locked anymore. When you first pull out and stop in the dock (where you see the tunnel in front of you and the people in line on your right)....get ready. As soon as the car is released and starts moving press play. Enjoy.