You’ll find it far easier to familiarize yourself with Flash MX if you already know how to use Flash. If you don’t, don’t worry. There are plenty of resources available for those starting at step one. The Flash MX development environment even comes with its own built-in contextual tutorials, which are pretty good. Macromedia frequently offers in-person half-day and full-day courses in major cities.

Articles:
Basic Concepts of Macromedia Flash MX
Coding Flash: Creating Movies with ActionScript
Coding for a Time-based Medium
Is this Flash a Little Brighter?
Flash MX Is a Big Step Forward
Drive your Flash Front-Ends with SOAP
Tutorial: Learning to Draw in Macromedia Flash MX
Tutorial: Learning to Animate in Macromedia Flash MX

Classes:
Technical Web Development PackageIntroduction to Macromedia Flash MX
Flash MX Developer Bootcamp
Macromedia eLearning CenterOnline Training

Good Links:
Macromedia eLearning Tutorials
DevX Macromedia MX Application Center
DevX web.design Discussion Group

Book:
Flash MX Bible, by Robert Reinhardt and Snow Dowd.