VS: How to show a messagebox in a ASP.NET application

The following class implements messagebox functionality. When calling this function a messagebox is shown and the current page is still shown. (often the messagebox functions create a blank form with a messagebox on top)

You can call the function at any place (because it's static) like this: Messagebox.Show("Hello World");

public class Messagebox
{
public Messagebox()
{

}

private static Hashtable m_executingPages = new Hashtable();

public static void Show(string sMessage)
{
// If this is the first time a page has called this method then
if (!m_executingPages.Contains(HttpContext.Current.Handler))
{
// Attempt to cast HttpHandler as a Page.
Page executingPage = HttpContext.Current.Handler as Page;

if (executingPage != null)
{
// Create a Queue to hold one or more messages.
Queue messageQueue = new Queue();

sMessage = sMessage.Replace("\r", " ");

// Add our message to the Queue
messageQueue.Enqueue(sMessage);

// Add our message queue to the hash table. Use our page reference
// (IHttpHandler) as the key.
m_executingPages.Add(HttpContext.Current.Handler, messageQueue);

// Wire up Unload event so that we can inject some JavaScript for the alerts.
executingPage.Unload += new EventHandler(ExecutingPage_Unload);
}
}
else
{
// If were here then the method has allready been called from the executing Page.
// We have allready created a message queue and stored a reference to it in our hastable.
Queue queue = (Queue)m_executingPages[HttpContext.Current.Handler];

// Add our message to the Queue
queue.Enqueue(sMessage);
}
}

// Our page has finished rendering so lets output the JavaScript to produce the alert's
private static void ExecutingPage_Unload(object sender, EventArgs e)
{
// Get our message queue from the hashtable
Queue queue = (Queue)m_executingPages[HttpContext.Current.Handler];

if (queue != null)
{
StringBuilder sb = new StringBuilder();

// How many messages have been registered?
int iMsgCount = queue.Count;

// Use StringBuilder to build up our client slide JavaScript.
sb.Append("<script language='javascript'>");

// Loop round registered messages
string sMsg;
while (iMsgCount-- > 0)
{
sMsg = (string)queue.Dequeue();
sMsg = sMsg.Replace("\n", "\\n");
sMsg = sMsg.Replace("\"", "'");
sb.Append(@"alert( """ + sMsg + @""" );");
}

// Close our JS
sb.Append(@"</script>");

// Were done, so remove our page reference from the hashtable
m_executingPages.Remove(HttpContext.Current.Handler);

// Write the JavaScript to the end of the response stream.
HttpContext.Current.Response.Write(sb.ToString());
}
}
}