mojoPortal already includes jQuery from the google CDN. You do not need to add it, you just need to make sure any plugins you load load after jquery in the page. So you can't include the plugin directly in layout.master for example, you have to wrap it in a UserControl then add your UserControl to layout.master and that will make whatever is in your UserControl load after the main javascripts we include.
ie view the source of the rendered page and make sure your jQuery plugin is included after jQuery from google.
interesting plugin, I may look at integrating it myself sometime.
Hope it helps,
Joe