Administrator, Don is likely left over from a previous installation of Windows, so it provides a backup of that profile. Default is a template used to create new user profiles. Users should be the root folder of your profiles directory. Administrator is the system administrator account profiles (even if you an administrative user, there is still a system Administrator account). Don is your user profile.
Also if you set Vista to show hidden files, you'll see other system accounts like Network User, Public and others. These are hidden accounts that allow the system to function properly.
With Windows NT systems (so 2000, XP, Vista, 7, 8 and 10), you're never the only user. Windows NT is a multi-user system, so even when you use the system an no one else does, the system stands ready to create additional users. And many tasks are handled by other system accounts.
So the system is set up as it should be. You may wish to navigate the Administrator, Don folder and see if there are any settings files you may need to get a program working properly (that's a whole thread in itself). You should probably hang on to it for awhile until your sure, but it's not needed fro day-to-day operation of Windows.
