IE8, the follow-on to 2006′s IE7, was released in Beta 1 nearly three months ago. Since then, Microsoft has not specified a target for a second preview, although it has regularly posted progress notes and other information about the new browser on a company blog.

MacKechnie also told Web designers and site operators to start adding a compatibility tag to their site’s HTML code or those sites may not display properly when viewed in the new browser.

IE8, Microsoft said in early March, will default to a standards-compliant rendering of Web content — an approach that had been pushed by site developers — rather than a mode that stresses compatibility with IE7.

The new tag, which can be applied on a per-page basis or sitewide, instructs IE8 to display the content as would IE7.

“Browsing with this default setting [in IE8] may cause content written for previous versions of Internet Explorer to display differently than intended,” MacKechnie said. “This creates a call to action for site owners to ensure their content will continue to display seamlessly in Internet Explorer 8.”

The first beta of IE8 is not exactly in widespread use. According to the latest data from Web metrics company Net Applications, IE8 Beta 1 accounted for just .02% of all browsers used last month. IE7, by comparison, held the top spot with a market share of 45.9%.

IE8 Beta 1, which runs in Windows XP, Vista, Server 2003 and Server 2008, can be downloaded from Microsoft’s Web site.

The software maker said that a planned standards compatibility mode will now be the default rendering engine when IE8 makes its debut. Microsoft has already said that the new browser is capable of passing the Acid2 rendering test.

“We think that acting in accordance with principles is important, and IE8′s default is a demonstration of the interoperability principles in action,” IE general manager Dean Hachamovitch said in a blog posting.

With IE8, Microsoft plans to have three rendering modes: the new standards-compliant mode, the IE7 rendering engine, as well as an option for displaying older Web sites. Because of the default shift, Web sites that want IE8 to use its IE7 engine will have to add a tag to their site’s code.

Microsoft noted that there are some legal reasons for changing course. “While we do not believe there are currently any legal requirements that would dictate which rendering mode must be chosen as the default for a given browser, this step clearly removes this question as a potential legal and regulatory issue,” Microsoft General Counsel Brad Smith said in a statement.

At the end of last year, Opera complained to the European Commission about Microsoft’s browser practices, and last week Microsoft was handed a record fine for its past noncompliance with EU dictates.

Microsoft hasn’t said when the final version will be out, but a beta version of the browser is due out in the first half of the year. There also will likely be more browser news later this week, when Hachamovitch gives a keynote speech at the Mix08 conference in Las Vegas.