Users trying to access Microsoft's MSN.com with a non-Microsoft browser are finding themselves locked out. While the software leviathan's Internet Explorer easily reaches MSN, other browsers -- such as Opera and Mozilla -- run into trouble. Using the most recent browser from Mozilla.org to reach MSN brings a message from Microsoft saying it has "detected that the browser that you are using will not render MSN.com correctly." Mozilla.org does open-source browser development for AOL Time Warner's Netscape Communications unit. "Additionally, you'll see the most advanced functionality of MSN.com only with the latest version of Microsoft Internet Explorer or MSN Explorer," the message continues. The page then provides several links for users to download versions of Internet Explorer for Windows, Macintosh and MSN Explorer. Microsoft could not immediately be reached for comment. Norwegian browser maker Opera Software confirmed on Thursday that it had noticed its browser was unable to access MSN.com. Several readers also alerted CNET News.com. "Microsoft is actively keeping our browser from accessing MSN.com," said Jon S. Tetzchner, Opera's chief executive. He added that every time a browser connects to a server, it sends a string to the server telling it what type of browser is seeking access. "Microsoft is seeing (that) it is an Opera browser and shutting it out," said Tetzchner, whose team was testing the problem Thursday. "If you change the Opera string by one letter, it is letting us in." Microsoft today launched its newest operating system, Windows XP. The company had previously announced that, on the same day, it would also give MSN.com a face-lift to make it run faster as well as offer more entertainment and news content. A move to favouring Internet Explorer over other browsers would give Microsoft considerable leverage as it prepares to jump into the world of Web services. Through its .Net software-as-a-service strategy, Microsoft hopes to sell software by subscription, and either directly or with a partner, offer a wide range of ancillary services, ranging from online calendars to financial and travel services. Through Windows XP, MSN is emerging as a major end point for delivering those services. The majority of Microsoft's most popular products link to MSN in one way or another. Office XP, for example, features a pull-down, get-more-info menu feature called Smart Tags that connects to MSN. Microsoft had planned to include Smart Tags in Internet Explorer 6 but pulled the feature. Financial programs Money and Great Plains also lean heavily on MSN features. Besides launching MSN as the default home page, Internet Explorer 6 replaces the more typical "page not found" with an MSN search page. Windows XP is chock full of MSN hooks. The Internet search feature from the Start Menu uses MSN. Windows Media Player drives traffic to MSN, as does the Passport authentication feature found in Windows Messenger. The Photo & Camera Wizard, where users can order online prints from digital images, also directs traffic to MSN. See the Windows XP Resource Centre for the latest news on Microsoft's new operating system. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the Microsoft forum. Let the editors know what you think in the Mailroom. And read other letters.