Making alternate stylesheets?

I am looking into making two style sheets that a user can choose - the first one would have paragraph text set at 12 pixels and the second stylesheet would have paragraph text set at say 16 pixels. So in my html page I could have two links - one saying “click here for normal size text”, and another link saying “click here for large text”

Simple as that. But i read through this tutorial:
[COLOR=#0000ff]http://www.alistapart.com/stories/alternate/[/COLOR]

I simply cannot get this to work - I downloaded the javascript file and tried to follow along but when i test this in the browser, nothing happens.

Can you help me on this one?

Thank you.