This is possible to do in many few ways. How I would do it (I'm not suggesting it's the best way, it's just the way I think is the path of least resistance) is going to be to setup a page on your WordPress site and use a custom page template. That template can include everything you want to include, and then you can use curl, file_get_contents, or another method to grab it over http. I would recommend making this template output XML and wrapping your elements appropriately. For instance,
<elements>
<siteheader>...</siteheader>
<sitemenu>...</sitemenu>
</elements>
When you download the XML file, you'll want to cache it so that every phpBB page hit doesn't also require a hit to your WP site. In your phpBB code, you would parse the XML and use the parts as needed.
I would do it this way for three reasons:
- By loading the file over your domain, you'll always retrieve the correct content from the correct blog and not have to worry about setting the global blog_id, etc.
- This affords you the ability to scale horizontally and put phpBB on one server and WP on another someday.
- Your system will be more orthogonal, which makes it easier to maintain and test, as well as being generally more agile.
I hope this is clear enough; I can provide more examples if needed.
Cheers~
