Need Internet help.

I use airport. We have two networks, both with passwords. I also have one network that I also get that doesn't have a password. Problem is, whenever I use iChat, it just starts logging in and out so I can't use it for a while. That only happens when I am on that network. Also, for some reason it keeps just going to that network by default whenever I close my computer and open it up again. I could just use Adium, but I wouldn't like to always have to go without the video-chatting. I could remove it, but then I would be without it when my internet fails, which it usually doesn't when the others do. What should I do?