Here's a post from Daigoro's note re: headsets and mics for Macs:
"Topic: Mics and Headsets for Ventrilo
Looking for a headset? The sound input jack on your Mac is not a microphone input jack, even though it's the same size. You must use your Mac's built-in Mic (with headphones) or a USB headset (or possibly a bluetooth headset, but I have no experience with that).
If you use the built-in mic, don't use external speakers, otherwise others will hear an echo (their own voices played through your speakers and then captured by your mic!). Instead, use headphones or earbuds."
I actually use a headset with attached boom mike that I plug into my Mac's mic jack - and it works pretty well. In fact, Daigoro, you commented on Vent how I was one of the rare people to pronounce your name correctly! In my older system, the built-in mic is down near the keyboard, so it picks up any keystrokes in addition to ambient room noise. In contrast, my headset mic works great with no background noise.
The headset I use is a Labtech C-324, and I'm running a PowerBook G4 with OSX 10.3.9. Anybody else find similar experience?