The window disappears when you take the cursor away.
During the beta test only 50% of readers to sites testing the feature will see the ads - it’s some kind of controlled test.
To participate in the program you just need to be an affiliate as far as I can see - log into the associate’s page and you should be invited to join the beta test.
For More info visit Amazon..
Product previews do all this – and keep visitors on your Web site until they're ready to buy. Product previews are a portal into Amazon.com, directly on your Web site. When users hover over a preview-enhanced link, a small window appears containing valuable content and information about the product you're advertising, including an image, new and used price, average customer review and availability. It also gives your visitors the ability to add the item directly to their Amazon.com shopping cart.
Forty Associates recently added product previews to their Web site as part of a small beta program. During the beta, visitors to Associate sites who viewed a product preview clicked through to Amazon.com nearly 4% of the time. Those clicks resulted in a purchase over 6% of the time.