Looping circles

I'm sure this is a pretty simple animation but I'm fairly new at Flash. I want to create a movie clip consisting of concentric circles emminating out from a single point. How would I go about this? Is there a tutorial somewhere online that would show me how to do this or something similar? I can get one circle to enlarge but my problem is how to put three or four circles into the mix and turn it into a continous loop? Something like this (though my circles will just be outlines but it's close enough for me to figure out how it's done).