I'm guessing I was the first to incorporate Ant into the Arduino world ... and I'd like to help you depending on your level of autonomy.
Processing offers really interesting possibilities. A few years ago we built a custom Arduino board with an AP2 module on the board itself. The board took analog signals and converted them to digital and sent the result out via the AP2 module.
All the code to do this has been tested and works on the Arduino. I found it very awkward to work with the AP2 chip as a hobbyist. There is nothing easy when it comes to trying to solder this chip to a board by hand. In the end we had a few dozen boards made by a local supplier.
Back to Processing. I'm at ease with Linux and OSX. The ANT dongles are not easy to work with on OSX. And when I say not easy, they do not appear in /dev when you plug them in. On Linux, with some clever modprobe'ing they show up in /dev. Then they work really well. I use the "Suunto" mini dongles. Regardless of the supplier, they are all the same.
So if you are on Linux, we have half the battle won. Next, communicating with the ANT dongle is fairly simple once you know what bits to send. All of this is documented. If you've built your own sensor, then you know how to decode the payload. If you are trying to figure out what an HRM is sending or a Power Meter, then you are left with the ANT+ documentation.
I am a "full patch" member of the Ant Consortium. So I get all the documentation I need. I'm not sure what you get when you are an "adopter". Unfortunately I cannot share this information without proof of your standing. The ANT+ key was once a closely guarded secret. It may still be. I don't know. Without it, ANT+ will not be available to you.
I can imagine some really nice looking "dashboard" or "head unit" running in Processing. If you are entitled to the ANT+ documentation, etc., I can show you how to proceed.
Best regards,
Allan