468x60 pixels file size: 10K or smaller graphic
format: *.gif only, animation ok
Max File Size of 10K File size must be no
larger than 10K, or 10,000 bytes of memory. You can check the size of your file
by opening the directory where you saved the graphic. The size of the file is
usually listed next to its name.
GIF animation OK
Your banner may contain animation that is built using GIF graphics. The file name
of your banner graphic must end with the '.gif' file extension. Your banner cannot
include Active HTML, Java graphics, or Real Audio.