In System-->Configuration-->Packaging, click Software Media Manager. After putting in your root password and allowing it to update, you will be presented with a list of your software sources. Highlight each one in turn and click edit to see what each one says. When you come to the one which looks for the cd7, remove it. It will then stop asking for it.
Alternatively, go to
www.urpmi.org/easyurpmi and use the instructions at the bottom of the page to remove all your update media, then use that page to add new media.