David,
Computerworks is right. Your browser has been hijacked, possibly the result of what we call a "drive-by". I would oridinarily recommend Spybot but they haven't had an update in a while so go to http:\\
www.lavasoftusa.com and download the latest build of Ad-aware 6.0. Once you have it installed, make sure to let it check for updates. Then, launch the cleaning process. When it's done searching and you go to the page that lists all of the spyware components found, right-click in the right hand pane and click on Select all. Then click next. Allow it to remove all of items. That will take care of your problem for sure.
Good luck and like some of the other guys said, don't monkey with the registry, you could end up trashing the OS.