Learning Advantage online training has a course that covers flexible body motion. I found the following course:
NX 10.0 Adding motion and defining the mechanism
Course description : This self-paced course contains 3 course modules and 1 assessment module. Prerequisite: Basic understanding of finite element analysis; Working knowledge of the NX Modeling application; ILT course:
Essentials for NX Designers (TR10051) or SP courses: NX Basics; Feature Modeling - Fundamentals; Assembly Modeling - Fundamentals
Mod. 1 Learn how to add motion to your mechanism and then view the results of the solution. Also, learn how to use features from the Assemblies application within Motion Simulation.
Mod. 2 Learn how to adjust the motion of your mechanism using objects such as springs, dampers, forces, and contact.
Mod. 3 Learn how to transfer loads to NX Motion Simulation from NX Advanced Simulation, define flexible bodies in your mechanism, include a PMDC electric motor in your mechanism, and run a Co-simulation using MATLAB Simulink.
Mod. 4 This assessment measures your knowledge of the topics covered in the Adding motion and defining the mechanism self-paced courses.
Learning Advantage is found in the training section of the Siemense PLM Software web site.