Shoutbox

Are you looking to open an xml click a button and have it sent it to the chat window that was just opened?

If you are opening the window from the Chat Window (via Menu or Command) you can store the Chat Window object to be later used or you can use the EnumWindows function and try and get the ZOrder of the window and which ever is first will likely be the top chatwindow. It is kinda hard to do what you are asking.