<UserControl x:Class="SilverlightApplication.HomePage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Grid Background="SandyBrown">
        <StackPanel x:Name="stackPanel">
            <TextBlock>Page from Host Application</TextBlock>
            <TextBlock 
                MouseLeftButtonUp="TextBlock_MouseLeftButtonUp"
                Cursor="Hand">
                Click Here to Display a UI from the Library Assembly
            </TextBlock>
        </StackPanel>
    </Grid>


</UserControl>

Imports SilverlightLibrary

Partial Public Class HomePage
    Inherits UserControl

    Public Sub New()
        InitializeComponent()
    End Sub

    Private Sub TextBlock_MouseLeftButtonUp(ByVal sender As Object, _
        ByVal e As MouseButtonEventArgs)

        ' Download an "on-demand" assembly. 
        Dim wc As New WebClient()
        AddHandler wc.OpenReadCompleted, AddressOf wc_OpenReadCompleted
        wc.OpenReadAsync(New Uri("SilverlightLibrary.dll", UriKind.Relative))

    End Sub

    Private Sub wc_OpenReadCompleted(ByVal sender As Object, _
        ByVal e As OpenReadCompletedEventArgs)

        If (e.[Error] Is Nothing) AndAlso (e.Cancelled = False) Then

            ' Convert the downloaded stream into an assembly that is 
            ' loaded into current AppDomain. 
            Dim assemblyPart As New AssemblyPart()
            assemblyPart.Load(e.Result)

            DisplayPageFromLibraryAssembly()

        End If

    End Sub

    Private Sub DisplayPageFromLibraryAssembly()

        ' Create an instance of the Page class in the library assembly. 
        Dim page As New Page()

        ' Display the new Page. 
        Me.stackPanel.Children.Add(page)

    End Sub

End Class

using System; // Uri
using System.Net; // WebClient,OpenReadCompletedEventHandler
using System.Windows; // AssemblyPart
using System.Windows.Controls; // UserControl
using System.Windows.Input; // MouseButtonEventArgs
using SilverlightLibrary; // Page

namespace SilverlightApplication
{
    public partial class HomePage : UserControl
    {
        public HomePage()
        {
            InitializeComponent();
        }

        private void TextBlock_MouseLeftButtonUp(
            object sender, MouseButtonEventArgs e)
        {
            // Download an "on-demand" assembly.
            WebClient wc = new WebClient();
            wc.OpenReadCompleted += 
                new OpenReadCompletedEventHandler(wc_OpenReadCompleted);
            wc.OpenReadAsync(
                new Uri("SilverlightLibrary.dll", UriKind.Relative));
        }

        private void wc_OpenReadCompleted(
            object sender, OpenReadCompletedEventArgs e)
        {
            if ((e.Error == null) && (e.Cancelled == false))
            {
                // Convert the downloaded stream into an assembly that is
                // loaded into current AppDomain.
                AssemblyPart assemblyPart = new AssemblyPart();
                assemblyPart.Load(e.Result);

                DisplayPageFromLibraryAssembly();
            }
        }

        private void DisplayPageFromLibraryAssembly() {

            // Create an instance of the Page class in the library assembly.
            Page page = new Page();

            // Display the new Page. 
            this.stackPanel.Children.Add(page);
        }
    }
}