They were ones that existed before the reinstall. Perhaps on other installations. But they only show up when I go to properties>security. Not elsewhere. To get rid of them, I would have to delete them from every folder these ghost usernames have access to, which is basically all of them.
Quick update: I did actually disable UAC. This has helped somewhat, but only when doing routine tasks, like copying files with the regular windows copier. If I try to use Teracopy, it doesn't work. If I run an older program that doesn't give itself admin privileges/does whatever magic newer programs seem to usee to not have to do this, it won't work.
The only thing that has fixed this so far is marking the directory as writeable to 'Everyone.' This seems like a bad move securitywise, though, as this means when I share a folder over my network, my friends can put files there. Which I don't mind generally, but some of them like to prank >_>