Check out this article, this will help you
In this article, i used to open a window. it is not a modal
window. to open a modal window, window.showmodaldialog instead of
Microsoft India Community Star,

"Northern" <> wrote in message
> I need to write code in my command button ASP server
> control click event handler to do a few things. The last
> one of those things will be open a pop up browser window.
> I also want this pop up window to be in modal mode. In
> another word, the user can't go back to the parent window
> before close this one out.
> I searched a lot of resources but still couldn't find a
> way to do this.
> Could someone show me how to do this?
> Thanks a million!