Ok... More Info.
Silverlight is a plugin for browsers that enables them to run rich internet applications. Silverlight, as of 1.1, contains the full .Net CLR, which means you can use any .Net language to develop Silverlight applications.
Silverlight was code-named Windows Presentation Foundation/Everywhere, and as Ayman said tonight, Everywhere means the web. Silverlight provides a subset of the WPF capabilities, so you can use animation, vector graphics, videos, and any else you can do with normal WPF applications, only on the web.
Now, if you want to develop Silverlight applications, you need the Orcas beta, and Microsoft Blend 2 (May preview).
Mohammed Abbadi
Microsoft Certified Skeptic
Program Developer (C#, Java, Common Lisp)