[Giaguara]

remove the buddies in ichat buddy list. choose the buddy, hit delete key and answer YES for removing it.
you have to be connected to do it.
you don't have to touch your address book.

aim, yim, icq etc have problems when using with third party software. so e.g. proteus or fire allows you to ADD buddies but not to REMOVE them.
i have used ichat with a .mac account, very rarely with aim.
and with it the remove buddies works.

don't remove anything from address book. just log in ichat, and select all the buddies from your buddy list that you want to remove, and hit delete. that should do it.