Leo says that something is taking up a great deal of RAM and it's causing the computer to labor hard and slow down. "Services" are just things running in the background. He can examine what services are running to get an idea of what's slowing down his computer by right clicking on "My Computer", then click "Manage", and click the "Services" tab. This will show him a list of all the services that are running. Windows may also be indexing the computer at bad times.
Process Explorer would also tell him what is running on his system. Or he could run Task Manager (by pressing "Control-Alt-Delete"), click on "processes", and then right click "Service Host".
He should make sure he has at least 4GB of RAM. He can find out how much RAM he has by right clicking on "My Computer".
Malware could be a culprit here as well. He should run the Malicious Software Removal Tool by clicking on "Run" from the Start menu, and typing "MRT".