There is a very simple way to add Silverlight to SharePoint if you use the Silverlight Streaming service by Windows Live.

Here are steps to follow:

1. Get the contents into Silverlight Streaming by Windows Live (see the Getting Started section in the SDK for more information)
2. Add a Content Editor Web Part to the SharePoint site
3. Set the source of the content Editor Web Part (in the browser) to contain an iFrame
   • For example, you can use the following to try it out:

     <iframe src="http://silverlight.services.live.com/invoke/6579/WLTVSEMEAREHEARSAL/iframe.html" frameborder="0" />

4. View the page and the iFrame will instantiate a Silverlight application inline.

That's it!

Reference: Angus Logan's Blog