Seeting a cookie to close a popup window

[JRAY]

I have this piece of code to open my Flash intro:

var introWindow;
introWindow=window.open("Intro2.htm","Introduction","width=550, height=390"
introWindow.moveTo(200,200);

I'm not a programmer, so I need some help with cookies. How do I get the intro window to pop up only once in a session?

Thanks!