setPixel transparent

programming flash
1

I am trying to use the bitmapData.setPixels method to set certain pixels in the bitmap transparent. But no matter what I do, it always seems to set the pixel(s) black (non-transparent).

Here is my code:

[AS]
bmpd = new ImageFromLibrary(0, 0);
bmpd.setPixel(0, 0, 0x00000000);
[/AS]

Anyone have any idea on why its not setting the pixel(s) transparent?

Thanks in advance