Many folders used by earlier versions of Windows have been moved to a new location or given a new name in Windows Vista. However, the old folders can still be seen if you have enabled Show Hidden Files, and they look like this: Notice they are displayed with a transparent icon and a shortcut symbol.
Although these look like folders, they are actually what is known as a junction. Junctions behave like shortcuts, but look just like regular folders.
Their purpose is to silently redirect programs that access them to their Windows Vista equivalent.
Since junctions aren't really folders, it is not possible to access them, and any attempt to do so will give you an "Access Denied" error.
Here is a list of all of the folders that have been moved in Windows Vista, along with their new location: