Although Flex 2 and Flash 9 player are official out, Flash 9 is still at least one year away from being released. You might like to try out Adobe Flash 9 Public Alpha first.

Here is a nice document regarding ActionScript 2.0 Migration, it lists out all differences between ActionScript 2.0 and ActionScript 3.0.

For example:

clearInterval() = flash.utils.clearInterval()
fscommand() = flash.system.fscommand()
getURL() = flash.net.navigateToURL()
gotoAndPlay() = flash.display.MovieClip.gotoAndPlay()
loadMovie() = flash.display.Loader
startDrag() = flash.display.Sprite.startDrag()