hook implementation on voting event

Hi
I am lost,
i'm looking at both the vote_up_down and votingapi module codes, and I really am stalling.
i'm using the vote_up_down module on my site

I need to write a hook to perform an action each time a vote is cast. (or tallied actually, it doesn't matter that much, but cast is preferred)
which direction should I be looking into ?

- should I call a hook or a callback function ?

- should it have the form mymodulename_vote or something else ?

thank you