> Is there a way to set an ActiveRecord object to point to a table  
> with a
> multi-column primary key?

Not really, no. Active Record was designed for a single column  
primary key and that assumption runs pretty deep. AR is not a Data  
Mapper, so you have to be within a reasonable vicinity of its  
assumptions to enjoy it.
--
David Heinemeier Hansson
http://www.loudthinking.com -- Broadcasting Brain
http://www.basecamphq.com   -- Online project management
http://www.rubyonrails.com  -- Web-application framework