$NTUninstall - What are these folders?

The $NTUninstall directories are hidden in the Windows folder. They are the backups of files overwritten or modified by all of the Windows hotfixes and the like that you get periodically from Windows Update.

They can be deleted without any worry, but it's not really necessary. The only times that I bother removing these folders is when I'm about to do a virus scan that I'm in a hurry to get finished, or when I'm running out of disk space.

You will no longer be able to uninstall the hotfix once you delete it's referenced folder.