I've got a website where just about all the content is in a flash movie. Is there anything I can do to improve my search engine ranking or make my content more indexable?
Yes you can. This article explains it fairly well.
My opinion on the matter (take it or leave it)
It is a real pain in the butt in my opinion. I would highly advise you to abandon an all-flash website. Take the time you would put into making it SEO-friendly and rebuild it using HTML.
A few links on Flash SWF file indexability:
What Google has to say is:
I've never seen significant search traffic to Flash files.