I recently installed a Netgear WG311 Wireless-G PCI network adapter to a pc that was formerly using the Windows XP Fast user switching ( the login screen that allows you to simply click on your user name to login).
“A recently installed program has disabled the welcome screen and Fast User Switching. To restore these features you must unistall the program. The following filename might help you identify the program that made the change: mrvgina.DLL”
HKEY_LOCAL_MACHINE/Software/Microsoft/Windows NT/Current Version/WINLOGONThen remove the key named GINAdll
The next login I was back to my fast user switching screen.