You just add all your code to your silverlight project (Download Web Developer 2008 and Silverlight SDK). Then in MainPage.xml, or what's it's called you add this where you see height and width efore >: xamln:Game="cls-namespace-GameNamespace".
Then in the gap: <canvas> <Game:Game1 x:Name="Game" /> </canvas>
Then you need to add a folder called Content and all your other content folders in it. When that is done you have to change the properties on your .xnb files to Content in the dropdown list.
You also need to add the SilverSprite library or dll to your project (Don't forget t add reference to it!). Then you just add the library to your using statements ex: using SilverArcade.SilverSprite; Don't forget to add the IO namespace.
Plese tell me if something isn't right, or doesn't work!