While Silverlight and SharePoint integration is not an OOB experience for developers today, there is a tremendous interest from business to add the rich interactive application experience to users. To use Silverlight in a SharePoint environment, developers can rely on two SharePoint customization approaches, web parts and custom web applications that are running within SharePoint sites, to accomplishing the goal. Below are several examples on how to create Silverlight enabled web parts for SharePoint applications.

http://www.liveside.net/blogs/developer/archive/2007/12/05/add-silverlight-to-sharepoint-2007.aspx
http://www.harbar.net/archive/2007/04/24/Silverlight-Field-Control-for-Office-SharePoint-Server-2007.aspx
http://sharepoint.microsoft.com/blogs/mikeg/Lists/Categories/Category.aspx?Name=Silverlight
http://www.codeplex.com/bjsspv
http://www.codeplex.com/SWPS

An easy way to introduce Silverlight to SharePoint without coding is to use the Content Editor web part with an iframe. See detail at
http://dev.live.com/blogs/sls/archive/2007/12/10/176.aspx or http://dev.live.com/silverlight/