MVP Nick Whittome authored Microsoft Knowledge Base Article 555377 - Device manager reports myriad "unknown devices" after upgrade from Windows XP SP1 to Windows XP SP2, which explained how incorrect registry permissions on the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum key could cause the screen to almost fill with new device found messages.

I have confirmed that you can resolve this problem, before or after the upgrade to SP2, by running the following Corrected version of SubInAcl command:

subinacl /subkeyreg HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum /grant=Administrators=F /grant=System=F /grant=everyone=R
NOTE: I was able to run the above command while logged on as a member of the Administrators group. If that doesn't work for you, run the command by scheduling it with the AT command, which will run it in the System account context.