You can video chat with either other iChat users (have to be using a mac w/ a camera) or you can videochat to other AIM users (I think currently just the new PC version of AIM supports this). Last week I was using iChat and video chatting with a friend using AIM on a PC. It is probably thinking you are trying to use a Jabber account, and to the best of my knowledge, you can only video chat to others using either iChat to iChat or iChat to PC AIM.
So I guess the question is.. are you trying to videochat with another iChat user? A PC user? A Mac user? If it's Mac, they have to be using iChat (and have a built-in or firewire camera); if it is to PC, they have to be using AIM. Unless Google chat and Jabber support this, I do not have information on that...