You could use this website:
http://mybannermaker.com/
This method is a little different but it works. If you go on the website it's pretty much self explanatory. Use Full Banner or Half banner. Those fit within the resolution limits. After you make your banner click the option to download it. You're gonna need a Photobucket account. From there upload your picture then copy and paste link...I'm trying to remember if it's direct link or IMG link...I think it's IMG link. But yea that's it. If you need me to give you step by step instructions just reply back.