Microsoft Internet Explorer for Windows, versions 5.5 SP2 and 6.0 (soon to be released) no longer support Netscape-style plug-ins, such as the plug-in installed as part of QuickTime 5.0.2 and earlier versions. Consequently, Windows customers using these versions of Explorer may be unable to view QuickTime content in the browser. Mac users and Netscape users are unaffected.
To restore compatibility, Apple has provided an ActiveX control. By visiting this page you will be prompted to download and install this control if you do not already have it. Alternatively you may check your installiation at: http://www.apple.com/quicktime/download/qtcheck/