Stop! .png is actually much more than some kind of gif format. Actually it could well be the internet file format of the future, because it supports 256 shades of grey in alpha. The result is that, for instance, an image on a webpage can be partially transparant and have a transparant soft shadow. Flash can use png images and the best part is, there are two kind of them, the one that resembles .gif (256 color) BUT the other one can have all the colors and transparancy you want AND it is lossless! No artefacts! When you open a .png file, it will be transparant in Photoshop. So that is a good start. When you option-click on the layer (I think it is the same on PC, otherwise use the whatever-key/click combination that makes a selection based on the transparancy of the layer you are in), make a new layer and fill the selection with black. Throw away the layer containing the original image, flatten and save under a different name. Sounds like something you can automate, doesn't it? option-clicking is absolutely necessairy, the magic wand (which I honestly NEVER use) doesn't do half-transparant selection, nor does it select transparant parts inside the layer. The .png format is read by newer browsers as well, but not enough to use a lot on the web. The negative side of doing things with them .png files is that they are rather small, most of the time. So zooming in on parts you texture with them will usually result in blocky textures. The larger the better!