If you're in Creo Parametric 5.0 or 6.0, you can get a free 20 day trial of Creo Simulation Live. It is ANSYS embedded in standard part and assembly modes for performing structural, thermal, and modal analysis in real time as you are designing.
Here is a video showing some modal analysis:
Get your free trial today! You can sign up from the Live Simulation tab and it will install the necessary license configuration right on your computer.