One of the students in my visual anthro class asked about how to capture an iChat video conversation (both sides). She wanted to tape a conversation with one of her informants. A little googling revealed a neat little application called Conference Recorder:
There are also some neat tips in the article, including the use of SnapZ or Garage Band to record iChat (and perhaps Skype) conversations.
As always, let the other person know that you are recording the conversation -- for ethical and legal reasons.