Well, if it is simple enough, powerpoint itself can move some objects around in basic ways if I recall. You might want to try that first since it will take the least amount of time to get working to your satisfaction. If you require something with a little more capability, then there are all kinds of flash based animation software and/or compositing software. How much time are you willing to climb a learning curve? If I had to do it, I would use Proshow Producer since it is good at slide shows, video as well as keyframing animations. But then again, I know it so... Adobe also has a lot of capable, bloatware products if you want to go that route too.
"Swish" is a cute and fairly easy to use flash animator.
Of course, I only make suggestions that I can provide links for.