Forest Pack simply uses the animation applied to the source geometry, so in this case you would want to animate the 3 individual blades of grass used to create Forest_Clump from the first tutorial. Make sure you set the parameter curve out of range type to loop for each so that the animation doesn't stop. Then set the following settings in the animation rollout: turn on "Random from Geometry", and set time offset=20 and samples=4. Do this for the nested and main Forest object.
Hope that makes sense.