I went to Fry's to buy a headset so I could play TF2 without having to stop every once in a while to /type/ things at people. I found one I really liked, the plantronics .audio 370. And the only one they had was open. So I bought a 360 instead, which was almost as nice.
What I did NOT buy was anything to convert from microphone-level to line-level, and the mac pro only has a line-level port. Which I think I /knew/, but didn't even look before I left to remind myself.
And now it's too late to go back out, without having to lock up the dog.