Creating a Flash map with transparent png's

Hi everyone, I’m trying to create a rollover flash map of England. In the past I have simply got a map image, traced over each section and saved as a button with a rollover effect, job done.

However this time I have the various counties within England as individual png’s with transaprent backgrounds. I have converted each of them into rollover buttons and every single button has its own layer on the timeline, but the problem arises as the mouse detects the square box around each png image, ignoring the transparency.

I want the ‘hit area’ for each button to just be non-transparent part of the png.

I have seen ‘InteractivePNG’: http://blog.mosessupposes.com/?p=40 but am not great at actionscript and can’t get it to work.

Does anyone have any simple ideas on how I could get round this problem? Thanks for our help.