GIFs vs PNG

Is there a way to use straight GIFs (using an image location) rather than PNGs for the various images?

When does AW use the icons.png rather than the control png (grid, checkbox, ...)? If I created my own png, how would I have AW use it rather than the standard AW pngs?

Thanks for the info. It did take a little doing but I was able to define my own graphic definitions specifically for my application and have them point to .gif files in my own directory instead.