Great start!
Tis' a little bit laggy in places though, like you said. Fixing that is a question of what you want to lose in terms of details. There was alot going on in the backgrounds, just like the scene in the actual movie, but it will cause lag in a web flash. I find it's best to use .png pics for any background stills rather than symbols or stage work in flash.
Also, it's best to "stream" your music rather than the event/start options, but remember you can't stream across different scenes.
Go to the newgrounds forums, click on the big forums button at the top of the page and do a search on "streaming music".
This flash was still awesome :)