Portamento is a jQuery plugin that makes it simple to add sliding (aka "floating") panel functionality to your web page. All that's needed is some simple CSS and one line of JavaScript, and you're away!
It works fine with floated and absolutely-positioned layouts, in all modern browsers and some not-so-modern ones too.
Portamento also has sensible behaviour if the user's viewport is too small to display the whole panel, so you don't need to worry about users not being able to see your important content.