Hmm... I tried making a little JavaScript, but I don't know if this is what you want...
http://shoutbox.menthix.net/banner.html
When you first go there, you should see the MP2 banner, then any time you refresh within the next day, it won't be there (the cookie expires in a day). Also, the cookie's path is set to "/" so it should apply to all pages on the domain.
Just put the HTML for your banner inside the document.write() with quotes escaped... it's a pretty simple script.
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