Have a look here - http://mochaui.com. Or more generally - here, or even more generally - google for an AJAX UI library.

Dude.

Don’t.

No unrequested windows, save for rare edge cases like help windows (which by definition aren’t unrequested). They’re user-hostile (in fact a usability disaster), the mark of an assholish and incompetent Web developer, and, for good measure, a WCAG violation.

Next you’ll be asking us for help typesetting a novel in Arial.

—
Joe Clark
http://joeclark.org/

I once read a novel typeset in Arial. After about 100 pages I wanted to rip my eyes out and after 200 pages I wanted to rip the author's eyes out. It was a self-published novel, and a decent story, but I'm really hoping if he ever finishes his next novel that he asks for help with the typesetting and doesn't do it in Arial again.

I think there's a time and place for pop-up windows, myself, but Joe is most astute than I am, in general, so I'll defer to his opinion.

If you are referring to the 'click to see bigger picture' type of behavior that opens a large image on the page itself, that's going to be what is commonly called 'lightbox'. There are various scripts out there to accomplish this. If you're using jQuery, there's the 'thickbox' clone.

The big problem is really the definition of what a "new window" is. Using the standard desktop browser scenario, it's easy to understand that it opens a separate instance of a browser window. But when you're using a handheld device, or a screen-reading device, or a text browser, what consists of a new window? Your design needs to account for that.

Old-skool pop up windows can serve certain specific purposes, but it should be as Joe said not "unrequested". As long as the user has a choice, or isn't forced into opening a new window, they can be used.

Given what you are asking for, which isn't very specific, the more specific term that aluminum is speaking of is technically known as a "modal window" and can, and should be, quite accessible. Lightbox, Thickbox, Greybox, they're all just different implementations of a modal window that doesn't open a new instance of a browser window. All simply display a part of your page that already exists, or is requested through AJAX, and hopefully all information is otherwise accessible to those not using javascript.

Hope you find what you're looking for!