Saucy >>> Unobtrusive Styling Plugin

The idea is to use javascript to style DOM elements using images
rendered according to the certain style rules also specified in the
HTML. This normally involves pointing the background image to the
rendering script on the server using RMagick.

It's currently available as a rails plugin :

ruby script/plugin install http://saucy.googlecode.com/svn/saucy

read more here :

http://weblog.parkerfox.co.uk/2007/1/2/saucy-unobtrusive-styling-framework