I don't seem to have a problem saving my images as .png files. Poser 5 and 6 saves them with a transparent alpha channel. I offere poser 'tubes' to the graphic community and I have them in .png format. Until a couple weeks ago I hadn't heard of anyone having any problem using them. Someone contacted me saying that when they open any of the .png files into their graphic program that it has a background...when it shouldn't. I suggested that if that was happening, that after opening the image in her graphic program, that she should go to her selections area and "load from alpha channel" and it would clear away the background. It worked for her. I'm not sure why she and your friend are having that problem with .png files, but loading from alpha channel in the graphic program might be the fix she needs.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi