Newbie - How to give a button a rocking effect on mouse over

Hi everyone I am a real newbie when it comes to using flash as have never used the application before.

I have tried looking through the tutorials for what I am looking for but to no avail. I am embarking on a mini solo project (building my first website) and I wanted to give my buttons a “rocking” effect on mouse over.

I am already able to do the simple on mouse over change colour etc so wanted to try something different.

Any help would be extremely appreciated.