Your site within Tripod or Geocities is probably a wonderful website. However, most often, banners placed at the top of the page are just spam.
Advertisers are interested in only one thing, getting readers to their sites.
In my humble opinion banner exchange programs are doing you a grave disservice. If you don t want people to read your content, don t put it up there. If you SELL ads in the form of banners, that might be another issue. However consider that when your reader clicks to that advertisers' site, they're gone. You can't even realistically count that visitor to your site.