Ultra new?! Don't you worry. A lot of long time AS2 users
feel the same way as you. There sure is some new ground to cover
with this release, but it's all for the better.
Actually you
should think in terms of importing the classes you use in
the project, but Flash CS3 lend you a helping hand here. It imports
and knows all class imports that starts with "flash" (are there any
other classes imported, anyone?).
LoaderInfo() is a class created in the main timeline of any
loaded SWF-file on stage. It contains all the properties needed to
identify base look-and-feel (width, height, frame rate, swf version
etc.). root (no underscore in AS3) can still (in this example) be
used to reach the main timeline, and the loaderInfo is available
before the INIT.
The Loader() class has a property called contentLoaderInfo
there can get the information about the file being loaded into the
loader.content property.This is the most used way of preloading,
because the loader can reuse the preloader on several movies. The
way I showed you it perfectly legal, but you have to implement it
on all movies to be loaded.
All the best