We had an issue when connecting with a Zero Client to a windows XP pool
After logon , we got immediately a black screen.
When touching the mouse everything was back to normal.
Because this happened immediately after logon, this was confusing for a lot of users
Cause: Registrykeys: ScreenSaveActive and ScreenSaverIsSecure in .Default users
Solution : After changing Registrykeys: ScreenSaveActive and ScreenSaverIsSecure in HKEY_USERS\.DEFAULT\Control Panel\Desktop both values to 1 the problem went away
see also : http://support.microsoft.com/kb/314493