Hi Splatty - we're actually working on this right now. We're planning to add the option for you to select the offers you want to display within the widgets we have in the Ad Wizard.
Until we get that up and running, you can use the Ad Wizard and target with keywords, you can create your own stand-alone offers with anything you find in the offer catalog or on your partner TradePub page, or you can as your account manager to create a banner or promotion for you.
I hope that will be done server side, so we can put the code on our sites, and then alter what it shows through revresponse interface. If not, it's hardly worth the effort.