Ok, the main question I'd have regarding that setup is, what are all the different blogs powered by?

* a single Wordpress install
* multiple Wordpress installs
* a single WPMU install

Without knowing the above, what I can tell you is that you'll be able to show the ads throughout the whole site (or other sites, if you wished) using a single OIO install.

What the answer to the above question will determine is whether you'd be better off installing OIO as a Wordpress plugin, or as a standalone app.

If all the blogs are powered by a single Wordpress install, then you can use OIO as a Wordress plugin. If it's using WPMU or multiple Wordpress installs, the best route (so that you only have to install OIO once) would be to set it up as a standalone app, then use javascript to display the ads on all parts of the site.

In that case, you need just install it as a Wordpress plugin, then use the standard php output functions to show ads on any part of the site that uses Wordpress.

I'm not too familiar with bbpress, but I presume the Wordpress engine isn't loaded when bbpress loads. So for the forum sections, the easiest solution is to use the javascript option to display ads - although there is a php integration guide available for non-Wordpress apps if you prefer.

OIO does have an an inbuilt ad zone category selector (see the advanced settings section). This means that you can assign an ad to a Wordpress category and it will only display in that category (and any posts in that category). This saves you from having to create a new ad zone for every category - it can all be done through a single zone.

For other pages (non-category), you'd need to create a zone for that page. For example, you could create a zone and call it "Home Page Ads" - then display that zone only on the home page using Wordpress conditionals.