Transparent .png's online...

Hi,

I have some forums online, which I decided needed a new theme to go with the site, so I created a blue one. But the problem was my old style was white, so some of the images had white backgrounds around them. But then I found out that .png's supported partial transparency (i.e. if i had a shadow, it would make a darker shade of whatever colour it was ontop of). So i fixed up all the images, and it was looking great.

But then I remembered that I was using FireFox, so I went to look at it in Internet Explorer, and it was terrible. All the transparent parts weren't transparent, but a light shade of blue. What I want to know is, is there any way I can save .png's so that their transparency works on both Firefox and Internet Explorer?