Microsoft just release Silverlight, which is basically a interactive media technology that is similar in functionality to Adobe's Flash. Here is a excerpt from the site: "Silverlight is a cross-browser, cross-platform plug-in for delivering the next generation of media experiences and rich interactive applications (RIAs) for the Web."
Silverlight is a browser plug-in for Internet Explorer, Firefox, and Safari. The plug-in will run on Windows XP SP2 & Vista (on IE and Firefox) or the Mac OS X (on Firefox and Safari). You can download the plug from this page.