You have to use ManualResetEvent for such things. Initiate event and
pass it to an asynchronous method. When a method complete job it have to
invoke Set() method. While an asynchronous method completing execution,
a synchronosu method should invoke WaitOne(). Here is pseudo code for you:

AsyncLogon(ManualResetEvent event)
{
   try
   {
      ...
   }
   finally
   {
      event.Set();
   }
}

SyncLogon()
{
   ManualResetEvent event = new ManualResetEvent(false);
   AsyncLogon(event);
   event.WaitOne();
   event.Close();
}

HTH

--
Sergey Bogdanov [.NET CF MVP, MCSD]
http://www.sergeybogdanov.com