Really. If you send me a PS3 I'll be happy to do some "testing" with it to make sure it works!
In all seriousness, it seems like they still have a lot of work to do on the web browser. From what I've just read, iffy Flash support and virtually no AJAX support... which means web 2.0 features (like the chatbox) are not going to work very well on the PS3 web browser.
Unfortunately there's not much I can do to make this work better for your right now --- I'm sure that the PS3 team is working hard to get their browser up to speed, so that it can support features like the ChatBox.
Sorry it's not working for you yet.... looks like you're stuck with the computer. If you're able to watch the show on PS3, great! I would recommend watching the show in full screen, and use your laptop to interact with the ChatBox. My friend had his laptop plugged into a widescreen TV for last night's webcast, so we could watch it in full screen... i used a laptop to run the ChatBox and this worked well.
Thanks for pointing this out.