UI Dialog on Rails can't find image files...

I've downloaded jquery and the jquery ui for dialogs, both seem to work fine except:

The thick-close x doesn't show up on the right hand side of my dialog title. Apparently it can't find my images. I'm running Ruby on Rails and I put the image files in #{RAILS_ROOT}/public/images.

I've searched around but at this point I'm pretty clueless. Any help would be appreciated.