The unist.exe probably didnt work properly.
Unist Is a special file that keep a log of where and how to remove all the files in the application.
Sometimes when you try to remove a program that is in use (its virtually locked into the memory) and cannot be removed, thus when when the uninst program trys to remove the files that are in use, windows rejects access until reboot.
It main term is called "Memory Resident".
There is a series of steps to do this properly so bear with me....
First of all we need to disable the download manager.
Reboot you computer and wait until the inital screen(just after you turn it on), just after that continue to press F8 about once a second until a menu appears, Now using the arrow keys scroll down the one that says Safe Mode with Networking" and press enter.
When on your desktop open Internet Explorer and download the progarm again - you can download it because in safe mode you disable all 3rd party software and services(apart from norton coz its a bugger.
Now Download a program called ccleaner.exe, this is a powerfull free registry cleaner that will remove orphened keys accociated with IDM.
Now you have to rebuild the uninst.exe log file so you wil have reboot the pc in normal mode, and re-install IDM.
On installation it creates a special log file that lists EVERY file and REGISTRY KEY it installs.
Reboot the pc again and that will make sure that the program is finalised and fully installed.
Now the easy bit
Go to control Panel, Add Remove Programs, and then IDM.
When you click remove it will execute the uninst.exe in the IDM folder (usually something like c:\program files\tonec\internet download manager\uninst.exe)
UPDATE------->>>>>>>
Now for nview, i nearly forgot coz I was in my element.
As the post above, nview has nothing to with IDM, its just a enhancement application to use special features with your graphics card.