72826 theme changer

what i want my visitors to be able to do is click a link and dynamically change the 'theme' of the page (without reloading) i have already made the themes with css, i just need a way of dynamically switching them there will be four themes (possibly 5) a cookies would then be set so that the same theme would appear if when the visitor returns i dont know what language this could be written in (php/javscript?) so thats why its in more than one :) thanks -c0lin