After reading the Wall Street Journal description of MobileMe, I realized that it may have been installed with the latest version of iTunes. Sure enough, it is was in the startup file, and when I unchecked it, the mobile device helper message disappeared from iTunes, even with the User Account control turned off.
You can find your start up menu by typing msconfig in the search box, clicking on the icon that appears, and then navigating to the start up file. I unchecked a number of other programs that had been installed with downloaded software,including iTunes itself. I'm OK with manually starting it.