Filtering Items in a List: ALL checkbox?

Hi, I’ve used Kirupa’s Filtering Items in a List tutorial and it worked just great for me… thanks so much for making it simple enough for a newbie with no JS experience (and still learning HTML) to use!

My question is, how can I include one more checkbox to this functionality, so that my users can check or uncheck an “ALL” category? My list is an extensive list of publications with links, and I’m using your filter to sort the pubs by theme/topic. But since I’m using six categories, it’s kind of a pain to uncheck all of them, and then recheck them all if the user wants to see the entire list.

You can see what I’m working on if you click the Publications link on my test site here: http://kpepplertest2.site40.net/.

Thank you! Janis