An accordion can be quite a tricky component to implement, even for someone with a good knowledge of ActionScript. As such, rather than wasting time attempting to write one yourself, I would suggest you find a third-party component you can use.
There are probably an abundance of free, third-party component sets out there, but you might start by having a look at minimalcomps by Keith Peters which includes an accordion component which sounds like it might be a good fit for your requirements (ie. there is no transition on the expand / retract). You can see it in action here and the code behind it here.