Upon reviewing several topics related to Battle.net's .smk Banner Ad's, I have come to the conclusion that there is no useful information for supporting these files! The SDK costs a lot of money, but every good programmer has their methods of avoiding such issues ;).
I have decided to make this SDK information available for public use, here: http://highbrow.webhop.net/cgi-bin/ISAPI.dll?funct=smacker
Please note that newer game clients may use .png and .mng files. You can find information on these files on this topic: http://forum.valhallalegends.com/phpbbs/index.php?topic=6367.msg56130#msg56130
Since the other thread on this topic is locked, I had to create a new one. Please use this topic for feedback on your questions/concerns for this information.
Hope this helps, enjoy!