Not sure what you mean. An AIM buddy list is housed in the AOL servers and travels with you so whenever you login to AIM, your list is there for you ready for use. No real need to copy it anywhere.
iChat keeps your buddy lists separate for your different screenames, and as far as I know, there’s no way to change that. You can use a different chat client to accomplish the unified Buddy List- Adium does this particularly well.