i think i've found a way to rotate banners using jQuery Cycle.
the site is already loading the jquery.cycle.all.js script cos i'm using Meteor Slides - if yours doesn't, find a way to load the script, probably through your functions.php or another slideshow plugin.
all you need then is to set your WP Bannerize widget to show more than 1 banner (of course) and to target the group's css class with the jQuery Cycle function:
fx: 'fade' // choose your transition type, ex: fade, scrollUp, shuffle, etc...
(you could, of course, target all of your ad widgets by using the .wp_bannerize class)
for more jQuery Cycle effects and settings, visit: