I started out using the exact same size as the originals, which was 24x24 pixels per icon. After trying your suggestion of importing the images, skin studio created icons that were 25 pixels high, but still 24 pixels wide. For the small version, I just put in 16 pixels for the height, and kept the same aspect ratio.
The first time I went from 24 to 25 pixels high, there were no lines under the explorer set, but it came back the next time. I also tried using TGA with a clear background. When I tried doing PNG with a clear background, I had to flatten the layers and it went white.
What I am using now is the same gray as the buttons to surround each icon.
More info than you asked for, but I thought it might save some questions down the line.
Doug
