Add image-banner in threadbit

[Pokeropoly.it]

Hi,

it's my first post in this forum so I apoligize if i do something wrong.

I would know if there's any plugin for adding an image or a banner in the threadbit. if it doesn't exist, how could I modify the template?

Here you can find an image as example:

http://img824.imageshack.us/img824/473/bannersej.jpg

Thanks.