I'm new to Ruby and Rails, too. Chris' example is very cool - I hadn't seen "Module.const_get" before. A less sophisticated (and much more dangerous) way to do the same thing would be to use eval:
x = "Foo" obj = eval("#{x}.new") obj.class => Foo
Actually, good Rubyists can manage to construct whole classes (and modules and definitions) on the fly, not just objects. Cool stuff.
Jim