I never do Jules, but it seems to me I've read that some people do. . I have no idea why that would happen, but I can ask the tech people if they know anything about it for ya. . .
Just yesterday I started getting these and I was really surprised. I hoped that it wasn't the DIS sending them out. My husband checked something last night and thinks it may have been that my sister signed up for Kazaa and it was bringing them.
The DIS does not have any advertising in the form of pop-ups. It sounds like you have some sort of Spyware - when you download things from the web they sometimes have these little advertising devils hidden within them as well.
The only free utility I know of is Ad Aware which scans your computer for various forms of Spyware and might take care of your pop-up problem. Be sure to read their FAQ first.