NMIndexingService.exe is a service that is part of the Nero Burning Rom suite, or more precisely Nero Scout which comes bundled with Nero 7 and Nero 8. If you have one of those applications installed check your task manager by pressing CTRL ALT DEL to find out if the NMIndexingService.exe process is running on the system.
This service is a indexing service that is being used by Nero Scout to provide fast access to the media library of the user on a computer. The real question is if it is beneficial to run an indexing service in the background all the time to speed up things when using Nero ? I would say that this is a waste of system resources (it can use more than 30 Megabytes of RAM when it's indexing files) unless the computer would be solely used to download and burn media.
NMIndexingService.exe can be disabled in the following way. First disable Nero Scout as outlined in the article that I have written last month. After that use the CTRL R shortcut, type services.msc and search for the NMIndexingService in the list.
Make sure that service is stopped and set to either disabled or manual. To change the state right-click the service and select Stop if it is still started or select Properties to disable the service completely.