I know a little. I'm assuming you are referring to either DesktopX or ObjectDock. An ico file is an icon format that is used for well .. icons. IconPackager displays icons. Programs usually include an ico image so windows can display an icon on menus and such. ico files are scalable and range in size typically from 16 pt to 256 pt. A png file is a graphic image file (non-layered) and like ico files can include alpha levels(transparency) A png file is not limited in size and an ico file is limited ..to 256x256 and scaled downward(256,128,96,64,48,32, and 16 I think). Most graphic paint programs allow you to save files in a png format but not in ico format. Graphics programs that allow saving in ico format are designed specificly for icon image making. IconDeveloper can take an image file such as a 256x256 or a 128x128 png file and convert it to an ico format. In fact I think there are a fair number of icon skinners who develop icons in a png format and then use IconDeveloper to convert them into a standard ico format for use with IconPackager. A png file can also have a variety of shapes and sizes and is more versatile in that regard. Many of the graphics images you see in DesktopX themes and ObjectDock themes are png file images. I hope this answers your question.  

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