I have done this with the jQuery Slider without much trouble.
Read the docs here: http://docs.jquery.com/UI/Slider
Drop this in your controller/form/whatever:
Add an appriopriately ID'd <div id="myslider"></div> in your template, create and init the object in the myslider.js file:
// Prototype doesn't like $
// Prep the slider
You should be off and running like a trademarked green tractor manufacturer's mascot.