An app to video chat with a Mac and iChat?

not sure if this works in the way you're asking, but have you checked out fring? or skype? the mac users can definitely download skype, not sure about how fring works exactly.

 

Try IPWebcam in conjunction with AIM on your computer. It takes a little setting up and I still haven't officially tried it yet but the whole purpose of IPWebcam is to make your phone the webcam...