My Diablo 2 fucked up randomly and wouldn't start so I uninstalled it, but there are some files left over in the Diablo II folder that I want to get rid of so I can just start fresh. However, when I try it tells me I need permission to do this even though I am the administrator. So what gives?

I am running Vista.

You'll have to set yourself as owner, and replace the permissions on the folder as well as every file and subfolder in it.

http://www.mydigitallife.info/2007/05/25/how-to-take-ownership-and-grant-permissions-in-windows-vista/