gistfile1.rb

#app/models/chatter.rb
class Chatter < ActiveRecord::Base
  has_one :chats
end

#app/models/chat.rb
class Chat < ActiveRecord::Base
  belongs_to :chatter, :foreign_key => 'chatter_id'
end

#irb queries
>> c = Chat.find(:first, :conditions => ["chatter_id =2"])
=> #<Chat id: 1, chatter_id: 3, created_at: "2011-01-11 16:27:16", updated_at: "2011-01-11 23:27:34">

>> r = Chatter.find(:first, :conditions => ["id = #{c.chatter_id}"])
=> #<Chatter id: 2, name: "asfdsad", created_at: "2011-01-11 18:41:41", updated_at: "2011-01-11 18:41:41">