check whether child window is open from parent window - urge

[wxdqz]

Hi,

I have a intranet Application which uses a security system for authentication.

My requirement is that when a user logs into the application there will be link shown to the application.If the user clicks the link a window is opened which will be closed by the application developers and they will open a new window. which is the welcome page where the user can choose country and language.

Now if another user logs(using new browser instance IE) he will also see the application link and if he clicks the application ,at that time i have to check whether already a welcome page is opened ,if so i have to alert him saying that already a user has logged in and ask him to logout,otherwise if he is the first user and there is no welcome page open already then i should allow him to proceed as normally.

What i want to know is that how do i check whether the window (welcome page) is already open or not from the first window which i close say the file is index.html(opened first).

Hope my question is clear.Kindly reply as soon as possible

Thanks
Rama