XP windows explorer refresh problem

While in Windows Explorer, XP refreshes the screen (the mouse arrow turns to an hour glass, and the screen blinks). This happens at various times (sometimes it is every 10-30 seconds, other times it is every 5 seconds). It makes it very hard to browse, to copy or move files, and it makes Windows Explorer VERY SLOW - plus it is very annoying. We are getting ready to roll XP out to 400+ desktops, I do not want this to be an issue. Does anyone know how to resolve this problem? Thanks.