That`s great that you want to use eZ publish in your project!
You can add "text filed" data type to your class which can be use to display plain xhtml code or you can use match[node] for template override and paste your code in to tpl file.
Basically, you would put that javascript directly into an override template for the site.
It's the same as embedding an ad server script (which I assume is probably what you're trying to do).
If you're trying to pass around ad server stuff, I would HIGHLY suggest against embedding it for any kind of display. The best way is to manage it as an attached text file from your partners in eZ.