Replacing Header with an Ad

Link to my blog for examining: http://www.WhereIsHipHop.com/

I was wondering if there is a plugin that will replace the header of my blog (the picture of the city) with a 728×90 ad like this website does: http://www.2DopeBoyz.com/. We’re using the exact same template.

Style.css:

[CSS code removed per forum rules – the link to your site is enough]

Header.php:

[CSS code removed per forum rules – please folloow http://codex.wordpress.org/Forum_Welcome#Posting_Code for posting code]

Thanks in advance.