Recently set my dad up with a Mini, 28" screen, and Logitech webcam (the Mac-specific variant of the Pro 9000), and it worked perfectly. So yes, that should work just fine.
Two things to keep in mind:
One, if you're going to get a webcam it might be worth spending a bit extra on a good one. That particular Mac-targeted webcam does the autofocus and contrast adjustment in hardware, rather than software, so unlike most webcams, which rely on the (Windows-only) driver to handle tweaking and so only provide basic functionality on a Mac, it looks just as good on a Mac. I also tried Microsoft's highest-end camera, but, while it did work, it didn't look good at all due to not having a Mac driver to adjust the focus and light level.
An alternative is an inexpensive video camera (even an older one with a firewire output should work great). I've chatted with people using those before and the results are good. The notable difference is they're not nearly as wide-angle as most webcams (which are intended to have you right in front of them); if you're sitting way back from a big screen TV that might be a significant plus, rather than having tiny people in the middle of a large visible room due to a wide angle lens. You can also zoom in a bit to compensate for distance, if you want.
I also discovered putting a camera just under the screen, rather than above, makes it look a little more like you're looking directly at the person you're talking to, rather than below.
The other thing to be aware of is the sound; depending on how far away you are, it might be tough to get the microphone to register clearly without picking up a lot of echo from the speakers. One solution might be to have a separate desktop mic placed right in front of the people talking; this should minimize both problems with volume and echo (and you should be able to select the mic you want in iChat, even if the camera has one built-in). Alternately, having the camera much closer to the person than the screen and speakers might work.
