Wrong OS setting?

I was poking through my User Account Controls because I noticed that some permissions had changed when I noticed the Edit Environment Variables. In the space that names the Operating System (O S) it says Windows_NT instead of Vista.

I don't know that much about computers, but I know which OS I have and it ISN'T Windows_NT. It's just Vista Home Basic.

I have also noticed that deleted files and programs magically reappear about a week later and it's starting to freak me out but it's probably a glitch or something?

Anyway, I just wondered if I was looking at that setting right and understanding it.

Thank you!