Sorry for my english.
Yes is a big problem.... try to read the book "Ajax Patterns and Best Practices. Developing next generation of web applications". CHAPTER 9 State Navigation Pattern.
You can find the way to detect windows-tabs of the same browser.
Then Java Script function would look for all opened windows that contains a predefined piece of information such as html body id and If such common marker is found that means we already have window opened in which case we will pop-up Java Script alert notifying user that multiple windows are not supported yet.