I'm not 100% on this, but I think it may be the Indexing Service which is supposed to make searches of your hard drive a lot quicker. To turn it off, open 'Computer Management' from 'Administrative Tools' (on the Start menu if you enabled this, or from the Control Panel). Select 'Services and Applications' and double click on 'Services'. Find the Indexing Service and double click to bring up the Properties window. Click 'Stop' to stop the service. From the Status type drop down box select 'Disabled', which should ensure that it doesn't appear again.
Let me know if this solves it.
Marc