What are prfXXXX.tmp files and how do you get ride of them? Please help

Hello everyone. Every few weeks, a roaming profile on our network accumulates files called prfXXXX.tmp located on the desktop. These files are 2 gigs in size each. Does anyone know what these files are; where these files come from, and how to prevent them from saving to the desktop or saving period? The network is a Windows environment running Windows XP as the Client and Windows Server 2000/2003. Thanks