(request) pop-up announcement upon webpage arrival

When someone arrives at my site, I would like a flyer for an upcoming class to pop up in front of my home page.

Is there a plug-in for that? I’m not sure of the technical terms and the keywords I searched didn’t turn anything up.

An example of what I mean is at http://www.ncnm.edu – though I don’t want mine to “automatically close after 5 seconds.”

Thanks for your help!
-Travis