<controls:ChildWindow x:Class="ChildWindowLogin.LoginWindow"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
           xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"
           Width="300" Height="200" 
           Title="Login Window"
           Closing="ChildWindow_Closing">
    <Grid x:Name="LayoutRoot" Margin="2">
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <StackPanel>
            <TextBlock Text="Name" />
            <TextBox x:Name="nameBox"/>
            <TextBlock Text="Password" />
            <PasswordBox x:Name="passwordBox"/>
        </StackPanel>
        <Button x:Name="CancelButton" Content="Cancel" Click="CancelButton_Click" 
                Width="75" Height="23" HorizontalAlignment="Right" Margin="0,12,0,0" 
                Grid.Row="1" />
        <Button x:Name="OKButton" Content="OK" Click="OKButton_Click" 
                Width="75" Height="23" HorizontalAlignment="Right" Margin="0,12,79,0" 
                Grid.Row="1" />
    </Grid>
</controls:ChildWindow>

Partial Public Class LoginWindow
    Inherits ChildWindow

    Public Sub New()
        InitializeComponent()
    End Sub
    Private Sub OKButton_Click(ByVal sender As Object, ByVal e As RoutedEventArgs) Handles OKButton.Click
        Me.DialogResult = True
    End Sub

    Private Sub CancelButton_Click(ByVal sender As Object, ByVal e As RoutedEventArgs) Handles CancelButton.Click
        Me.DialogResult = False
    End Sub
    Private Sub ChildWindow_Closing(ByVal sender As System.Object, ByVal e As System.ComponentModel.CancelEventArgs)
        If Me.DialogResult = True AndAlso _
                (Me.nameBox.Text = String.Empty OrElse Me.passwordBox.Password = String.Empty) Then
            e.Cancel = True
            Dim cw As New ChildWindow
            cw.Content = "Please enter name and password or click Cancel."
            cw.Show()
        End If
    End Sub
End Class

using System.Windows;
using System.Windows.Controls;

namespace ChildWindowLogin
{
    public partial class LoginWindow : ChildWindow
    {
        public LoginWindow()
        {
            InitializeComponent();
        }
        private void OKButton_Click(object sender, RoutedEventArgs e)
        {
            this.DialogResult = true;
        }

        private void CancelButton_Click(object sender, RoutedEventArgs e)
        {
            this.DialogResult = false;
        }
        private void ChildWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
        {
            if (this.DialogResult == true && 
                    (this.nameBox.Text == string.Empty || this.passwordBox.Password == string.Empty))
            {
                e.Cancel = true;
                ChildWindow cw = new ChildWindow();
                cw.Content = "Please enter name and password or click Cancel.";
                cw.Show();
            }
        }
    }
}

<UserControl x:Class="ChildWindowLogin.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="300" Height="200">
    <Grid x:Name="LayoutRoot" Background="White">
        <StackPanel Margin="5">
            <Button Height="23" Width="100" HorizontalAlignment="Left"
                    Content="Log in" Click="Button_Click" />
            <TextBlock Name="helloTxt" />
        </StackPanel>
    </Grid>
</UserControl>

Partial Public Class MainPage
    Inherits UserControl

    Public Sub New()
        InitializeComponent()
    End Sub
    Private Sub Button_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
        Dim loginWnd As New LoginWindow()
        AddHandler loginWnd.Closed, AddressOf loginWnd_Closed
        loginWnd.Show()
    End Sub
    Private Sub loginWnd_Closed(ByVal sender As System.Object, ByVal e As EventArgs)
        Dim lw As LoginWindow = CType(sender, LoginWindow)

        If lw.DialogResult = True AndAlso lw.nameBox.Text <> String.Empty Then
            Me.helloTxt.Text = "Hello " + lw.nameBox.Text
        ElseIf (lw.DialogResult = False) Then
            Me.helloTxt.Text = "Login canceled."
        End If
    End Sub
End Class

using System;
using System.Windows;
using System.Windows.Controls;

namespace ChildWindowLogin
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            LoginWindow loginWnd = new LoginWindow();
            loginWnd.Closed += new EventHandler(loginWnd_Closed);
            loginWnd.Show();
        }
        void loginWnd_Closed(object sender, EventArgs e)
        {
            LoginWindow lw = (LoginWindow)sender;

            if (lw.DialogResult == true && lw.nameBox.Text != string.Empty)
            {
                this.helloTxt.Text = "Hello " + lw.nameBox.Text;
            }
            else if (lw.DialogResult == false)
            {
                this.helloTxt.Text = "Login canceled.";
            }
        }
    }
}

<controls:ChildWindow x:Class="ChildWindowSplash.SplashWindow"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
           xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"
           Width="200" Height="150"
           HasCloseButton="False"
           OverlayBrush="{StaticResource overlayGradient}"
           OverlayOpacity="0.85">
    <Grid x:Name="LayoutRoot" Margin="2">
        <MediaElement x:Name="splashMedia" MediaEnded="splashMedia_MediaEnded"
                      Height="100" Margin="10" />
    </Grid>
</controls:ChildWindow>

Partial Public Class SplashWindow
    Inherits ChildWindow

    Public Sub New()
        InitializeComponent()
    End Sub
    Private Sub splashMedia_MediaEnded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
        Me.Close()
    End Sub
    Protected Overrides Sub OnOpened()
        MyBase.OnOpened()

        Dim generator As New Random
        Dim randomValue As Integer
        randomValue = generator.Next(0, 2)

        If randomValue = 1 Then
            Me.splashMedia.Source = New Uri("/Silverlight1.wmv", UriKind.RelativeOrAbsolute)
        Else
            Me.splashMedia.Source = New Uri("/Silverlight2.wmv", UriKind.RelativeOrAbsolute)
        End If
    End Sub
End Class

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Shapes;

namespace ChildWindowSplash
{
    public partial class SplashWindow : ChildWindow
    {
        public SplashWindow()
        {
            InitializeComponent();
        }
        private void splashMedia_MediaEnded(object sender, RoutedEventArgs e)
        {
            this.Close();
        }

        protected override void OnOpened()
        {
            base.OnOpened();

            Random random = new Random();
            if ((int)random.Next(0, 2) == 1)
            {
                this.splashMedia.Source = new Uri("/Silverlight1.wmv", UriKind.RelativeOrAbsolute); ;
            }
            else
                this.splashMedia.Source = new Uri("/Silverlight2.wmv", UriKind.RelativeOrAbsolute);
        }
    }
}

<UserControl x:Class="ChildWindowSplash.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="400" Height="300">
    <Grid x:Name="LayoutRoot" Background="White">
        <Button Content="Show Splash Window" Click="Button_Click" 
                Height="100" Width="200" Margin="10" />
    </Grid>
</UserControl>

Partial Public Class MainPage
    Inherits UserControl

    Public Sub New()
        InitializeComponent()
        AddHandler Me.Loaded, AddressOf MainPage_Loaded
    End Sub

    Private Sub Button_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
        Dim splashWnd As New SplashWindow
        splashWnd.Show()
    End Sub

    Private Sub MainPage_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
        Dim splashWnd As New SplashWindow
        splashWnd.Show()
    End Sub
End Class

using System.Windows;
using System.Windows.Controls;

namespace ChildWindowSplash
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
            Loaded += new RoutedEventHandler(MainPage_Loaded);
        }

        void MainPage_Loaded(object sender, RoutedEventArgs e)
        {
            SplashWindow splashWnd = new SplashWindow();
            splashWnd.Show();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            SplashWindow splashWnd = new SplashWindow();
            splashWnd.Show();
        }
    }
}