I'm building a flash site with 3d art using Swift 3d, and that's gonna be a big file as well when it's finished. A sort of way round it that I'm using is to have the main movie contain all art and nav buttons, and then load each page individually (with preloader) into a target movieclip on the main timeline. This won't reduce d/l time, but will get your site to the viewer faster initially, and the pages will cache on the viewers computer, so will obviously load instantly on the second view..

As for external software for compression, I've had a look round and can't find any, but u'll know about flashkit.com, there's a few good tutes on file optimization there.