First, I'd like to say that the project sounds really neat. Anything that mixes some motor control with software is appealing to me lately because I just used RS-232 for controlling some remote control car motors in a robotics competition.
It would be easier to understand if you could remove the unneeded information about things you can do on your own.
This is my understanding of what you want:
To put it in just a few words, you want to build a bridge between an RSS feed off Twitter and the iobridge api.
You want this work to be performed on the web server's computer.
If the server supports PHP, it can be used to download an RSS feed. It will likely support some XML parsing and processing functions too which can be used to extract the information you need.
Since you eventually want to use this iobridge api and twitter RSS feeds, I wouldn't do anything with the web server software, ie. Apache HTTP Server. Instead, I'd make a separate compiled program that runs on the same computer as the web server and continually downloads RSS feeds, parses them, and calls on the iobridge api as needed.
If you want users on the site to remotely control the devices in the tank, I would let the users send their commands from forms in the website and let the website's database temporarily store the commands. This way, the site acts as producer of tasks to be done. The compiled iobridge api program would then frequently ask for new jobs to execute like a producer-consumer pattern. The consumer would ask by downloading an XML or text based document frequently(every few seconds) and executing any jobs in them by calling on the iobridge api.