Still trying to post good Flex/3D app. tutorials whenever I find them. I have yet to use Five3D, however, it seems that many of these packages have more information on how to use them with Flash than Flex. When I started with PV3D, there was no readily available information on how to use PV3D with Flex.
This tutorial shows how to get started with Five3D and Flex. Seems that Five3D employs methods from the fl.motion package that is only available for FCS3. One day, I’ll have to look at that package in more detail and consider adding a complete set of equivalent methods to Singularity for Flex users.
Enjoy the tutorial!
The Algorithmist 
If you have Flash its easy enough to add those classes to you source path in Flex.
The operative word being ‘if’ – I don’t, for example, and many others that use Flex are in a similar boat.