With Internet Explorer 7 Beta 1 set to debut next month, Microsoft has quietly closed the door on Windows 2000 users planning to adopt the new Web browser.

IE7 will require Windows XP Service Pack 2 due to internal security changes that rely on Microsoft's latest operating system release.

The decision to update Internet Explorer before Longhorn arrives in late 2006 was announced by Bill Gates at the RSA Conference in February. Although Microsoft had said it was focusing on Windows XP SP2 only, the company did leave open the possibility of IE7 supporting Windows 2000.

But now, Microsoft says the task is too complex due to security features not available in the older operating system. Company officials also noted that Windows 2000 is moving into the "Extended" support phase of Microsoft's product lifecycle as of June 30, 2005.

"It should be no surprise that we do not plan on releasing IE7 for Windows 2000," IE program manager Chris Wilson wrote on the Internet Explorer Web log.

"One reason is where we are in the Windows 2000 lifecycle. Another is that some of the security work in IE7 relies on operating system functionality in XPSP2 that is non-trivial to port back to Windows 2000."

The decision brought mixed reactions, with some users agreeing that Windows 2000 customers should be making the upgrade to Windows XP or Server 2003. Others, however, noted that large numbers of users remain on Windows 2000, and developers would be forced to continue working around quirks found in IE6.