Silverlight extensions, does the client need them too?

I use Controls from Silverlight SDK and Silverlight Toolkit and I'm curious if the client has to install the packages as well?

How do I build such an application correctly to deploy it afterwards?

EDIT:

I just ask because I'm unable to get my application to run on a client running a bare SL4 runtime. It just throws the following exception:

Unhandled Error in Silverlight Application 
Code: 4004    
Category: ManagedRuntimeError       
Message: System.NullReferenceException: Der Objektverweis wurde nicht auf eine Objektinstanz festgelegt.
   bei System.Windows.Application.Application_Starting(Object sender, StartupEventArgs e)
   bei MS.Internal.CoreInvokeHandler.InvokeEventHandler(Int32 typeIndex, Delegate handlerDelegate, Object sender, Object args)
   bei MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)

I use the VS2010 devserver to deploy the application to the client.

The app makes use of a WCF Service I also serve by VS2010 for now, it also contains a "clientaccesspolicy.xml":

<?xml version="1.0" encoding="utf-8"?>
<access-policy>
  <cross-domain-access>
    <policy>
      <allow-from http-request-headers="*">
        <domain uri="*"/>
      </allow-from>
      <grant-to>
        <resource path="/" include-subpaths="true"/>
      </grant-to>
    </policy>
  </cross-domain-access>
</access-policy>

Thanks in advance.

Solution

You don't need to install those packages on the client side, it's will be part of your xap file,

and about the server running your Silverlight application, Silverlight is a client technology and can be hosted on any web server. It can be any type of web server that is capable of delivering the XAP file along with the correct content MIME type from the server (application/x-silverlight-app).
As long as it does that, we don’t care what type of web server it is delivering the XAP file.