Can you export a drawing made in flash as a transparent png in actionscript I know you can do it as a jpg with a white background but can you export the transparency?
Yes. Check out PNGEncoder in as3corelib (http://code.google.com/p/as3corelib/). Just take a snapshot of the MovieClip / Sprite that contains the drawing (make sure you create the BitmapData as transparent) and pass it to the encoder.
If you've just drawn the image in Flash and want it as a png then you don't need to export with ActionScript, just go:
File > Export > Export Image > Save as type > .png
I built a way to do this myself once. First I used bitmapdata.draw to convert it into a bitmap then looped through each pixel and got its value via getPixel32() (getPixel32 includes transparency getPixel() does not) and stored it into an array. Then I sent the very long array to PHP and used a loop to go through the array and reconstruct the image. Its not very efficient but no one at the time could tell me any other way to do so, and I was proud I figured out a way on my own.