The team sent private e-mail invitations to selected companies and asked them to spread the word.

On Thursday, Todd Friesen, owner of search engine optimization company Oilman Promotions, posted his invitation to test the service on his blog.

That led Yusuf Mehdi, senior vice president of MSN Information Services, to post the invitation on the MSN Search Weblog, extending the invitation to all readers of the blog.

MSN first tested adCenter in France and Singapore, with the official rollout in September.

The homegrown technology is designed to let advertisers take advantage of the audience information MSN gleans from its users across the network in order to better target keyword ads.

Advertisers will be able to refine their keyword buys by geographic location, gender, age group, lifestyle segment and time of day, combining data from Microsoft's Passport registration and purchased demographic information from partners, including consumer data bureau Experian.

MSN is specifically looking for small- to medium-sized businesses to participate in the self-service offering. Mehdi said beta testers would be able to access comprehensive data to plan more strategic campaigns, use advanced demographics to target ads, and be able to change campaigns on the fly.

The pilot remains by invitation only, he wrote, and Microsoft will select participants from those who apply.

MSN is expected to officially roll out adCenter in the United States in October.

During the U.S. pilot, MSN adCenter will deliver text-based advertisements on up to 25 percent of MSN Search traffic, Mehdi said. The remaining traffic will continue to be served through a partnership with Yahoo.

This article was adapted from InternetNews.com.