ChatAV webcam: iSight or a DV camcorder w/FireWire
Originally posted by IDANNY
Can I use a Pentax OPTIO S. to video chat with iChat
iDANNY, does your Pentax have a
FireWire port?
If not, Video signal cannot be supplied to your Mac.

No, USB won't work.
Does your Pentax have a built-in
microphone?
If not, Audio signal cannot be acquired.
Yes, you can use pretty much any DV Camcorder with a FireWire (iLink) connector and cable.
Or, you can buy the best Automatic focus/ light sensing, dual Microphone with background noise filtering, with special Mac mounts -- WebCam money can buy for only $149 (or, less for EDU if you're a student).
Get an iSight!
Otherwise, buy a $499 Canon DV CamCorder with built-in stereo microphone, and FireWire port (special Apple FW cable is $29 extra) and have the best of both worlds (video camera MiniDV tape recorder & a webcam)