boot manager HAS to start before loading a windows operating system. If you upgraded from Vista (or other OS) there is a chance that part of vista is still on your hard disk and the boot manager is responding to that. (There may also be a left over line in hte boot manager file telling the boot manager to offer this additional option.)As the previous reply indicates you need to look into the boot manager file and see what it is trying to do and then delete the line that is causing a second system to respond. Google really is worth typing in any question that tells of your problem.
'(eg: What should my boot manager in Win 7 look like