Rails - Aug 2006 - class validations - instance equivalent?

does anyone know if it''s possible to use rails validators from
validate()

I have some conditional validation to do, and using :if => Proc.new... on 
the class validators is getting messy, so I''m doing the condition
checking
in one place - validate() - except of course I can''t use rails
validators
there. I''ve started writing my own validators but I hate to re-invent
the
wheel.  any suggestions?

thanks
alan