Foreign Key Confusion

I'm confused on ActiveRecord, particularly where integration to legacy
DBs are concerned. I am hoping someone can point me to a reference that
explains foreign_key and association_foreign_key for me.

If I have a legacy MySQL DB with two tables specifid below, wherein I
have
a table, 'leads' which contains an index to 'origins' such that
leads.howdidyouhear=origins.id

CREATE TABLE `origins` (
  `id` int(11) NOT NULL auto_increment,
  `originname` varchar(60) NOT NULL default ''
)

CREATE TABLE `leads` (
  `id` int(11) NOT NULL auto_increment,
  `howdidyouhear` int(11) NOT NULL default '0',
  `amount` double NOT NULL default '0',
  `homeplan` int(3) NOT NULL default '0'
)

My problem is mapping this in active record. I am mapping it as follows
(I am
not certain this is correct, can someone please confirm? Does someone
have a link that explains this better to me? Thanks, Ike) :

class Origin < ActiveRecord::Base
  has_many :leads, :foreign_key => 'originname'
end

class Lead < ActiveRecord::Base
  belongs_to :origin, :foreign_key => 'howdidyouhear'
end

This should work for you

class Origin < ActiveRecord::Base
has_many :leads, :foreign_key => ‘‘howdidyouhear’’
end

class Lead < ActiveRecord::Base
belongs_to :origin, :foreign_key => ‘howdidyouhear’

end

Regards,
Jatinder