I've used MSIE, Firefox (deleted hosts file, disabled popup blockers, disabled fiirewall, enabled every kind of permission, etc...). Ad banner doesn't show up anyware.
Please note the following: Google AdWords Support and Google AdWords Support: Why can't I see my ad? If the daily budget of the advertiser falls below a certain level or if its targeted to viewers of a certain geographical areas it might not show, without regard to the site.. I think?