Don't use ESS or ODBC to connect to joomla or wordpress, the result may work but you're making it harder for yourself. Most of these CMS' have an API for accessing them, usually via Web Services. You then use HTTP calls from something like the BaseElements plugin to access them instead. www.goya.com.au/baseelements/plugin
This way, the complexities of the SQL structure are hidden and you get access to a simple interface for requesting data.
Thanks Nick for your great advice. How do you configure this?
It depends on the platform and the data your site is managing. Have a look for a module to do either a Web Service API or a RESTful Web service.
You essentially setup your website as a Web Service "server" and then FileMaker Pro becomes the client. You have a lot of configuration options in the server setup, so what you end up with will depend on what you want to do. Speak to your web developers to get an idea of the options available.
If you know what it is you want to acheive in terms of data flow back and forth, and know the platform details, we may be able to help a little more.