A PNG anti-aliased in transparent

To create an image like goo.png below, using Jasc Paint Shop Pro:

Create a new image, with 16.7M colours and a transparent background.
Draw on it in black. For this example, I used a black airbrush.
Mask – New – From Image: Source Opacity selected, Invert data off.
Mask – Save to Alpha Channel – OK – OK
The channel is called "Selection #0".
Save as .png, called foo.png. It saves it, with a warning to which I say OK.
Load it again. Paint all over it in black (this does not affect the alpha channel.)
Save it again, this time as goo.png.

works with 
Netscape 4NoPNG background is black instead of transparent
MozillaYesthanks to the help of Greg Roelof and others
Netscape 6Yesthanks to the help of Greg Roelof and others
Internet Explorer 6NoPNG background is grey instead of transparent
Internet Explorer 7Yes 
Opera 5NoPNG background is white instead of transparent
Opera 6Yes 

foo.png, anti-aliased in white

goo.png, anti-aliased in transparent
To see how smoothly the anti-aliasing of the
right-hand "G" image works, resize your browser
window, and change its width continuously.

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