That's what I figured. Internet Explorer doesn't properly support PNG files, which is basically an upgraded version of the GIF file, that allows a certain image that has empty space to show the background behind the image. Many graphic artists use this to make their work break through the confines of box art. I use Mozilla Firefox, which supports PNG files and shows it the way I meant for it to be show.
Re: Testing my new sig.
It is possible. However, once you break the confines of a rectangular image the parts that stand out become pixelated, especially if the resolution is high. It just doesn't look right. PNG files don't do that.
Re: Testing my new sig.
Kewl. I use Firefox part of the time, and the .png files look great there. I love the idea of not having to keep things rectangular, definitely.