I just completed a video tutorial on creating a bouncy-ball rig in blender 2.5
It is a good introduction to rigging a simple object for animating, and using drivers to automatically simulate things like squash-and-stretch. I split the video into 3 parts so it can be viewed on youtube, and it’s in HD so you can see all the settings.
The first part is - http://www.youtube.com/watch?v=p-zUyimSrVo - and the other two parts are linked from it.
Enjoy, and hope it helps.