PNG transparency

I found a section in memories here that partially answers my question. When I save images as .png and bits of them are transparent, the transparent part ends up only translucent white. (see my current icon) According to the memories entry, this is a screwy thing with Internet Explorer. I've had the same problem with .gifs, but that shouldn't be happening. Is it a browser thing? A photobucket thing? It only becomes a problem after I upload it somewhere. On my computer, it's perfectly transparent. Is there a browser it works correctly with? Mozilla?